I recently found out or thought I had found out what was giving me hives on my lower back and then it moves all over but mostly on back and thighs/knees. I had been taking different types of penicillan since March, of and on for a tooth that was absessed. After giving me another perscription, I tried to get caught up with the 4 a day (on the second day) after I took the 4th pill, I was broke out so bad, i thought I would have to go to the hospital. Benedryl does not seem to reach it unless I take two. I stopped taking the meds and alerted everyone I was allergic. I have not taken any since last Saturday Jan 4. How long does it stay in your system? and I was put on blood pressure meds last week. Reason being, I am breaking out again. Looking at information online, could my blood pressure med also be a cause of the hives or allergy? So why the heck does this make you believe it is free when now I have to pay for the answer. What a joke.