You most likely have cholinergic urticaria, or CU. Check out the "i most likely have cholinergic urticaria" thread in the Allergies and Asthma section. I have this condition to. From the other posts, it seems as though those with acne have a higher tendancy to develop this condition. The best thing to do is sweat everyday, go for a run or bike ride, bear through the pain, and it will subside. It gets better and better if you do this on a regular daily basis. Read the other thread for some more tips and advice.