Have you tried a gluten-free diet? I also suffered from intense itchiness following yoga practice (and lasting a few days!). It helped if I brought a spare shirt to change into following practice because I really couldn’t even drive home I was so uncomfortable. After going on a gluten-free diet, however, I noticed this problem went away completely. I can tolerate being in sweaty clothes all day where I couldn’t before. I have tried to add gluten back to my diet many times, but it wasn’t worth it. It also made my scalp itch. Good luck!