I Was Bit / Stung On My Upper Arm Sunday

I was bit / stung on my upper arm Sunday afternoon while hiking by an insect. Burn sensation and whelp immediately. Swelling, redness in a circle and red dots around that. As time has gone by swelling went down slightly but red ring has increased, covering most of my upper arm. Very painful and still burning sensation. I have taken Benadryl and an after bite spray to no relief.