What Do Red Rashes On The Abdomen And Chest Indicate?

I woke up yesterday with what I thought were spider bites on my scalp and on my one eye period as the day went along other things well I got red bumps and welts and rashes on my abdomen my chest area behind my knees and on the balls of my feet on my hands. I am 2 weeks post-op but have not started or stopped any medications and the last two weeks other than my Percocet period so I am wondering if this is some type of allergic reaction or if it s a medication interaction that maybe is just now hitting me period some areas work first started or already subsiding other areas are just swelling up. I ve been taking Benadryl and it seems to be helping is there anything else I should do