Why is my hair getting so poofy? :c

In all fairness I have really weird hair, like each strand is thin but I got sooo many, it's somewhere between straight and curly and tangles immediately after being brushed through if I change the parting or anything like that. But this heat is making it go completely crazy! It's all poofy now, completely tangled no matter how many times I brush it, it's like magic! It sticks out in all directions! This happened during the last heatwave too, what the heck is going on? :c