My Daughter Has Been Taking Doxycyline For 3-4 Months And

My daughter has been taking doxycyline for 3-4 months and expects to be on them to mid year. She has been suffering from constant numerous Boil's, as have I (she lives in Vic,I live in FNQ) 10 months is a long time to be taking antibiotics I believe. What deverse side affects should i be aware of or expect. Osca