My daughter is on an allergy shot maintenance program and had her monthly shot this afternoon. Around 2 hours later she was complaining that her arm was sore. Now 7 hours later, it continues to be sore, is red, hard and swollen. Would antihistamine be helpful at this point? Interesting, she has had shots now for close to 2 years, and this is the first reaction. Appreciate knowing if medication will help her through the night. Thank you. Karen