I gave myself an esophageal ulcer, by not taking enough water with the Doxy and lying down quickly after swallowing it. I've also had awful stomach pains and severe nausea (thought I was pregnant!) for a while. Eventually, I learned to take it after a little bit of food, and with lots of water and then it was manageable. Not a pleasant medication, but it does work for a while.
Is this your first time using an antibiotic? I have used many antibiotics before including doxycycline and feel that the only antibiotic that did anything for me was tetracycline. Tetracycline did give me a surprise years after taking it since I realized it had stained my wisdom teeth during the removal of the molars but the rest of my teeth were left unaffected and other than that I did not experience any other side effect. As far as doxycycline I did not have any side effect whatsoever and it did nothing for me but to be fair I feel since I had taken many antibiotics before I may have built resistance to antibiotics. I do think though that after having taken many different antibiotics I may have developed folliculitis which is only present after I shave since I don't get irritation but rather as my beard grows back I feel as though the hair itself causes redness but thankfully it's very minor and the "bump" itself is virtually painless and flat it's just the pigment which actually resolves in a couple days but I could be completely wrong and it could simply just be shaving irritation. I guess what I'm trying to say is that don't over do it on antibiotics. Hopefully doxycycline works for you but in case it does not work only take one more type of antibiotic and in case neither work it's best to give something else a try. I gave accutane a try and it worked wonders for me but it's definitely a very personal decision. I would have liked to have tried accutane years ago but unfortunately I did not know it existed and my "Doctor" at the time would only prescribe me antibiotics and topical medication despite me going countless times with every time praying that the medication he prescribed me would finally get rid of my acne. I actually remember one time going to an appointment and he prescribing me benzoyl peroxide and saying that there wasn't anything else he could give me. I would just like to recommend that you take medication as indicated and if you do have any side effects talk to your doctor and see what happens from there but most side effects should disappear after stopping medication if they do develop.