Itch when exersizing outdoors? Help PLEASE!

I wanted to know if anyone knows anything about what this could be.  I saw a doctor years ago and he basically said he didnt know, maybe allergies.  
Ever since I was about 17 this started happening when I went running...I would run for a while and then "the itchies" would start.  First it would be an EXTREME itch on the top of my upper legs.  I would run or walk and try to ignore it, but the itch would get deeper and stronger until I couldn't stand it and had to stop and scratch it.  It would feel better a second then it would spread to my hips, the rest of my legs, which again...I'd try to ignore, then the itch would become overwhelming and I'd scratch.  It would eventually spread all over my torso, legs, back, arms....but not my head.
I would run home with my entire body itching horribly, scratching as I would run, and then I would try to take a oatmeal bath, lotion, ice packs...anything!  But nothing would make the itch stop except time.
This never seems to happen when I go on the treadmill indoors and it didnt happen when I just go for a slow walk outside...normally.
Now I'm trying to go on walks with the baby in the stroller.  I was walking briskly today and it happened again!  I had to race home so I could just sit still so the itchies would stop.  I'm tired of this!  It's keeping me from excersizing!  Anyone have any ideas I could bring up to the doctor?? I've noticed doctors don't always think of everything...

[Schuyler_T]

Hello, first I wish to ask, have you noticed any physical indication after running, say a rash or hives? As the one thing I could think of is cholinergic urticaria, or hives activated by sweating and exercise among a few other things. its symptoms include Itching, burning, tingling, warm sensation preceding the onset of numerous small weals with surrounding bright red flares, with the rash often being very itchy. Also, have you ever noticed this same sort of itch after eating spicy food or taking a hot shower/bath? As those also could activate cholinergic urticaria.

One thing you can do temporarily is take an antihistamine before going out to exercise as this may help.

Good Luck