Random Occuring Rash NEED HELP!!!!!!!!!!!!!!!

Hello everyone, my name is Tyler from Las Vegas and I am 17 years old and wondering if someone could please help me out!!, About 2 months ago after spinning class at the gym I noticed a bunch of red dots all over my hands and arms, ever since then when I start to sweat i get this little spots on my hands, a little on my arms, on my chest and sometimes on my legs, but sometimes a couple of the spots will pop up for no reason or sometimes when i get nervous, after this rashes flame up, they tend to go away within the hour if i stop running or working out, the spots are red and not really raised but sometimes they kinda join up in a bunch, and a different more red rash occurs sometimes when i take a hot shower as well, i went to the dermatolgist but due to the lack of presence of my rash he couldnt tell me much so I hope somebody on here can he help me please, also lacrosse season has started and i was thinking it may be a bacteria in my dirty pads perhaps?  Im not sure, but please respond Asap because i am concerned its contagious and dont want my girlfriend to get it if it is. Thank you all very much.

[Bhupinder Kaur, MD]

Hello,
Cholinergic urticaria is an important possibility for your symptoms. It  is a form of chronic hives that is caused by an increase in body temperature. Take some antihistaminic like Benadryl or Claritin and apply some calamine lotion on the hives. If the symptoms persist then please get it examined from a dermatologist.

It is essential to rule out the presence of serious illnesses of which recurring hives can be a symptom. Examples are hepatitis, hyperthyroidism, lymphomas, collagen vascular diseases, and cancers of the rectum, kidneys and gastrointestinal tract.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.