Are there any over-the-counter products I could take to help with an allergic reaction (rash of red itchy red bumps all over my body?

Antihistamines. Depending on what the rash is from, you could try antihistamines like Diphenhydramine (benadryl). If you are having any respiratory symptoms like shortness of breath or throat swelling, you should be evaluated in the er.
Try hytone (hydrocortisone) cream. Of course you should first try to determine the cause..... If not severe(ie. No blisters , painful redness etc)try plain cortisone cream ..And take antihistamines....Not Benadryl (diphenhydramine) cream or any product containing benadryl (diphenhydramine).