Hi,
Thanks for posting your query at DoctorSpring.com. I am Dr.R.K and I am pleased to assist you.

Blackish stool indicates bleeding in the upper gastrointestinal tract.
Stomach pain, loss of appetite and upper GI bleed in a 22 year old may indicate peptic ulcer disease. An upper GI endoscopy may be done for confirmation.
The most common cause is H.pylori infection. So you should get tested for H.pylori infection.

NSAID (painkillers) is another cause for peptic ulcer disease. So you should try to avoid painkillers.

Also avoid smoking and drinking ( if you have these habits).
No, these are not symptoms of colon cancer.

I hope that answers your question.
Let me know if I can assist you further.
Regards,
Dr.R.K.

Hi,

H.pylori does not cause weight loss unless and until it causes cancer. If you have lost more than 10% of your body weight in 6 months time and if it was not intentional, then it is significant weight loss and needs thorough investigation.

Infection, malabsorption, hormone issues, malignancy are some of the causes of weight loss.

You can discuss with your doctor about these possibilities and get appropriate tests done.

Please let me know if I can assist you further.
Regards,
Dr.R.K

I would re-iterate what I suggested before -

Although, H.pylori is known to cause stomach cancer, but given your age the possibility of cancer is very less.

The semisolid stool could be due to infection or malabsorption or could be even due to irritable bowel syndrome.

A stool test and test for celiac disease may be done first. A colonoscopy may be done after that to look for causes in the colon.

Regards