Why can t I sleep even though I m exhausted.?

So school started the 5th so I haven t been able to sleep till noon unfortunately so the problem is I don t get enough Sleep. Every day I have dance for 1+ hrs (soon to increase) I also run everyday and usually do strength stuff as well along side a few hrs of homework and running off 3 hrs of sleep you would think I would pass right out but nope. I lay in bed till like 3-4 am and my body aches and I just wanna sleep but I just can t. So basically whenever I m in my room I just cry for no reason (I think it s because I m tired but I m not sure) so anyways I was looking for an explaintion as to why this happens and if there s anything I can do.