I have been on sulfamerh/trimethoprim for 17 days. Have been off for 3 days now I have a wierd rash on my arms and legs can this be a penn. Reaction?

Maybe Med Reaction. Trimethorprim/ sulfamethoxazole is a sulfa based antiobiitic. Not a penicillin derivative. That said it is still a common source of allergy. Talk to your doc. It may very well be the drug. If your having any breathing difficulty go directly to your nearest er.
Common problem. It is fairly common to get a rash after taking sulfa drugs. It is not related to a penicillin allergy. The "sulfa rash" is sometimes due to an allergy to sulfa drugs but not always. The typical sulfa rash is fine red bumps.