What Causes Patches Around Elbows, Forearms And Legs?

I am a 26 yr old female 5'5 and about 175 lbs, I have started to have flat patches of redness around my elbows, forearms, and my legs especially around my calves and ankles, My joints around my fingers, and my elbows are extremely sore.. I am begining to itch mostly around my legs and arms! all of which I have NEVER experienced before, this has been going on for about 2 days now. Any idea of what this could be? I am fairly healthy, over weight, but am toned and I am fairly active playing baseball 4 days a week and walking at least 2 days a week for about 45 mins..