It sounds like you have developed hives. Hives are swollen areas of skin in response to an allergy.
Some people have chronic ( meaning happens for a long time ) hives and itching. SOmetimes it is caused by allergans or cold weathe or just stress.
The Benadryl should help the hives and some people take other antihistamines that don't cause drowsiness such as Claritin.
Sometimes the hives are just a reaction to your itching but sometimes can indicate other problems such as hyperthyroidism.
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Let me know if you have more questions.