I Have Used One Tablet Of Dart For Headache 2

I have used one tablet of dart for headache 2 days before at night. after tiffin taken tablet and went for sleep. Suddenly, in midnight I felt itching and burning sensation in head and body and found some bumps in head and face and red rashes and swells on body. Next day I went to Medical shop and asked him whether tablet is expired, but he said it in valid. He has given me "ALLEGRA 120 mg". Eventhough, still I continue the problem. At present My fore head and both eyelids swelled and some rashes in body and face. Is this a severe problem or normal. Please advise.