Types of headaches symptoms and conditions

I am 18 years old and just recently started taking Doxycycline Hyclate through recommendation from a dermatologist. I feel very tired ALL the time and can hardly imagine being on this for much longer. I can't concentrate on the things that normally seem mundane and easy to focus on. I feel pretty emotional as well. Sometimes like crying for no reason. The worst part is the pressure I seem to be experiencing in my head. It's like a constant headache in the back of my brain. Not a sharp pain, but more of a air head effect.
Is anyone else experiencing these types of headaches?