((hugs)) sounds like your little guy has got a lot going on!

At age 7 (grade 1?), its not uncommon for kids to start being diagnosed for things like ADHD and sensory processing disorder. They've managed up to this point, but the additional stress of a structured classroom setting and full day school just kind of puts them over the edge. Like someone said above, have a chat with the school regarding an evaluation or take him to your family doctor.

I have more to add but will come back later to post.