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It doesn't mean that penicillin has entered your system unless you took a penicillin tablet. If you haven't taken any medication then it can't be penicillin.
However, you are probably allergic to something else you have encountered. Where the rash is on your body doesn't signify that "it is leaving your system." The hives are your skin reaction to something you are allergic to. It may be something you have eaten, or touched, a perfume (even someone else's), a cleaning product, etc.
You can continue to take Benadryl or other antihistamine (Zyrtec, Claritin) if the itching isn't too bad. If it gets worse, or you have difficulty breathing or swallowing, you should seek medical attention ASAP.