If my wife is allergic to penicillin and i take something that has penicillin in it, can we have sex?

Generally: But there will be some penicillin in your semen. If she has had a life-threatening reaction to penicillin, you should abstain; if she had a milder reaction, she should be prepared to experience some vaginal itching after intercourse (assuming, by the fact that you asked the question, that you don't use condoms - if you do, there's no problem).

Yes, but: It is not clear how much penicillin would get into your seminal fluid, if any, but to be safe, you should wear a condom when having intercourse.

Probably: Depends on the type of reaction she gets. If anaphylactic shock you had best see an allergist.