Annoying clothing

I have a 7 year old son who up until a a year and a half ago was the most easygoing child who would wear anything. When he started school things changed dramatically. It started with his underpants bothering him and moved onto pretty much every piece of clothing bothering him seams in socks are a problem too. He has one favourite t shirt which is ok one day and the next when he puts it on he has to rip it off because it is so uncomfortable. He is very affectionate but will wipe all kisses off. He is very easy to anger. I have tried OT, Bio medical testing and am waiting to see an allergist. Nothing I do seems to make much difference for him. I feel bad for him because it is so hard for him to handle. We have good days and we have very bad days. It just seems strange that it came on when he started school.

Could it go away as quickly as it came on or can an SPD come on at any time.

thanks