Hi I've been allergic too penicillin and antibiotics for years on Thursdays started with chest infection rang doctors he said I would be OK on doxycycline I've took 5 pills of far never felt that Ill had a constant really bad headache feeling generally off but was thinking I'm ok with doxycycline as I have no red rash as I usually get when I'm allergic but not in started vomiting so looked up side affects answer looks like I still allergic to all antibiotics... any advice???