What Causes Raised Rashes On The Back Of The Arms?

For last couple days I have had apparently an allergic reaction to something and don t know what. Nothing different I am eating no changes in any soap. Had been in the sun alot mowing beginning of wk, but did not get this after mowing which was beginning of this wk, it just started probably Wed and today. These are like raised welts back of arms it occurs and this morning whole tops of my legs with many of these what I call raised welts, alot of them and even back of buttocks. Have been using cortizone and also taking an allergy pill like benadryl. Very itchy. The ones this morning were alot of them and welty and itchy on top of legs, the other day just my arms had these same type I call raised welts then the arms went away and now today or morning all over my top part of legs and back part of them. After taking the benadryl type allergy pills and putting that cortizone eventually during the day the big welts aren t appearing and they go down. I have never had a type allergy that I know of, only sinus once in a while. The best I can explain is that when they come on they seem like clusters of raised type welts and many of them total itchy. The pills I am taking and the cortizone seem to be helping some. Could there possibly be something out now that I am getting in contact with that would cause allergic reaction. Thank you