The symptoms described by you such as facial swelling, nausea, fatigue, itching is probably due to the side effects of Doxycycline mono tablet. Doxycycline mono is used mainly for skin infections like acne. It acts by reducing the inflammation on the skin and the breakout of pimples. Usually the side effects are not so severe. The mild side effects would include nausea, fatigue, and headache that you are experiencing. But in view of the facial swelling and prolonged itching due to an allergic reaction, I would suggest you to use an antihistamine tablet like tablet cetirizine at bedtime for 3 days and a decongestant. The other methods are to use a mild face wash like Cetaphil to keep the skin dry. You can apply cold compression over the face for 10 minutes four to five times in a day to bring down the swelling .You can use extra pillows over the head to elevate the head and bring down the swelling. If the symptoms do not subside then you can consult your dermatologist.