could my hives be from a failed root canal?

almost 3 weeks ago I had a root canal done on my upper #5 premolar. A week after it was done I was back in the dds chair with the worst pain! the dds put me on penicillin and methylprednisolone for what im assuming was an infection although he never said it and said the root canal looked good. the week I was on the meds was the only time Ive felt normal. I went off the meds on a fri and by that sunday I was covered in hives and itching like crazy from head to toe! this has contenued daily for almost a week. I have no food allergies, basically i have no allergies to anything. I havent switched any products, soap, shampoo, lotions, laundry det, nothing! I havent even eaten anything out of the ordinary. Also since going off the meds Ive ran a low grade fever on and off, had heart palpatations of 120 times per minute while just sitting, and just an overall not good feeling. Its driving me crazy that my dds keeps insisting "everything looks good, youre fine"

I google HIves and abcess (abscess) and i found a few links that said yes an abcess (abscess) could casue hives...cus of the bodys reaction to the infection. my dds said nothing about a abcess (abscess) yet i have a knot at the base of the tooth and on my cheek and the dds said this is normal and will go away. the tooth still hurts to the touch 3 weeks later and all he says is normal and will heal. my dds also said a dental infection can NOT  cause hives. which is right the internet or my dds. Its just to odd of a coinscidense that the hives started right fater i ran out of the meds. Im going to make a new apt with a endo hopefully before the weekend to get new Xrays to see if there is an abcess (abscess) and put my mind to ease...My question is, if there is still an infection lingering can it be the root of my hives and itching and heck general ill feeling since i went off the meds?