My hair used to be curly and now it won't even curl. What's wrong?

My hair was thick and curly ever since I was born and my hair started growing. I've dyed my hair multiple times and it never really effected it until recently. My hair is now in between wavy and straight, but it just poufs out and gets frizzy (though not outrageously frizzy unless it rains or is humid out) and there's nothing I can do to it. I try curling it and it won't hold. My hair never used to be frizzy when it was curly. I used to straighten it, but now I rarely do because I heard that that may help it come back, but it's just not working. Is there anything I can do? I desperately miss my curly hair and am tired of just throwing my hair up in a ponytail because there's absolutely nothing i can do with it. is there any way i can get it back without getting a perm? please help!!!