Hey man, sorry about the late reply, I haven't been around here in awhile.
To be honest, I never really did figure out how. I ended up switching to Judo training instead of BJJ. I did some groundwork in Judo but it was primarily standing. I haven't had this weird itching thing in a long time, but it has been a long time since I've rolled for more than probably 5 or 6 minutes in one night. I did figure out that it only happens on exposed skin, though, so a rash guard helps.
hey I know the thread is old but I found the one about you itching the next time you sweat after practice. I have the exact same thing, have had it for years, and still can't figure out how to make it stop. You ever figure out how?