Thank you for the reply. That rules out one theory. The headaches started after April 4, 2014. They are not really headaches per se, but more like neurological sensations that start from the back of my neck and go to the top of my head. These sensations come and go, and feel like someone is tickling me from the inside, or a candle flame is burning on the inside of my head, but only on the left side. I also used to feel a pressure behind my left eye. My scalp would be tender also at various places at various times - sometimes behind the left ear, sometimes on my left temple, sometimes at the left trapezius muscle at back of neck. There are times when I would have hours or days of no sensation, then the sensations would flare up for a few seconds and then disappear, several times a day. I can induce these flare-ups if I pinch the left nostril. On April 4, I was with my girlfriend and I had licked her skin, with my tongue tasting something bitter. I didn't think of it then, but after the headaches started I asked her what was on her skin, and she said it was probably traces of personal lubricant - either water-based or silicone-based. After that evening was when all these head sensations started. Do you think these neurological sensations were caused by something toxic in the lubricant that made its way into my nervous system and settled on the occipital nerves? If so, I am surprised the symptoms would persist for over two months (although I have gone weeks without any sensations). The reason I used hydrogen peroxide to rinse out my mouth was my attempt to cleanse my mouth of any contaminate. I don't normally do this. In the few days after April 4, I did feel fuzzy-headed, and had difficulty breathing regularly and had sharp pain in the upper left side of my chest. I think this was a systemic reaction of some contaminate. There was no sensitivity to light, and my vision was not affected in any way. The systemic reaction has since gone away (no chest pain and no irregularity of breathing). Only the neurological sensations lingered and remain to this day. I believe these symptoms are chemically-induced because of a) the timing, and b) I never had any physical trauma to the head, neck, or any part of the body due to accidents, etc. so it can't be any sudden change in posture or such. I believe these sensations are the result of either inflammation of nerves or blood vessels, which could have been caused by the introduction of a toxic susbtance. By the way, I do have Heptatitis B and am taking Baraclude 500mg daily, but I do not belive that is a factor. I do not, nor does my family have a history of heart disease or diabetes. My father did die of kidney disease.

Thank you for your response. My symptoms do seem to point to a tension headache, but I have never had those before in my life. And I am not under any stress, which is known to cause tension headaches. Also, I have not noticed anything in my daily routine - poor posture, twisting of neck, etc. that might cause this as well. I will take your recommendation and use Ibuprofen for a week.

Here is my follow-up information. I did take Ibuprofen but only for three consecutive days, then for one day after that. There was pain relief when I took the Ibuprofen, but it returned as soon as I stopped taking it. Since my activity on this site, I have consulted two neurologists, and had an MRI done of the brain and spinal cord. Both did not show anything major to be alarmed about. The brain MRI showed T2 hyperintensity white spots in the left frontal region, but I was told that could be due to aging or is insignificant. The spine MRI showed slightly bulging discs at the neck C4 - C5. The neurologist said the discs may be the source of the pain, as I have complained of pain in the back of neck and shoulder as well, both on the left side. She prescribled Gabapentin but I am reluctant to take it (I have not taken it). The other neurologist I consulted said not to take Gabapentin as it is overkill and unnecessary.
Anyway, the MRIs and the two consultations with the two neurologists were ultimately inconclusive as to what is causing the headaches.
I know you originally said that this could be a tension headache, but honestly I am not under any stress, and don't have any emotional issues with family, etc. in my life.
The neck and shoulder pain could be a result of poor posture as I do sit in front of a computer all day, I got two professional massages, and even tried Chinese cup therapy. The latter helped with the pain relief. What cup therapy does is alter the circulation of blood in that part of the body, by freeing stagnant blood (per their literature), and since some of my headaches feel like it's circulation related (with the throbbing sore spots on scalp), the cup therapy DOES work, but only temporarily.
The MRI also indicated I do have mucus thickening at the maxillary and ethmoid sinuses. Should I see an Ear-Nose-Throat specialist? Could this be the cause of the problem?
I also had dental work recently on the right side of the mouth. My root canal and crown done last year got infected, so I went to a different dentist to have that re-done. He prescribled Amoxicillin which I took for 7 days. No relief from the pain in that time.
I also had an EEG and EMG done. I don't have the results of the EEG, but the EMG which was supposed to check for pinched nerve, indicated a mild problem with pinched nerve on the left side.
Should I go back and take the Ibuprofen for seven consecutive days? Will it stop the inflammation or just be temporary pain relief?
Any new thoughts with the additional information?