I feel hot but I don't have a temp.

Okay... this is going to sound really wiered... I randomly feel really, really hot, but I never, ever have a temp. I have a low body temp. I also get these really bad headaches but I can usually solve that by going outside to get some freash air. I get sometimes lightheaded. I'm 17 years old so I'm not going though menopause... speaking of which, my period use to be really heavy and only last about 7 days. Now it's always late, last for like 3 days and I hardly bleed... I thought it was just stress because of school, but I'm not sure anymore.... what do you all think? I'm not dehydrated because I always drink like 2 bottles of water in a row (when I can get my butt out of bed that is, it's gotten better, I drink more water now.) 
My fiends think that I might be gluten intolerant and lactose intolerant and I probably am but that doesn't explain my symptoms of; always feeling hot, but never having a temp, headaches with feeling lightheaded, and my period being messed up... any one have any ideas? 
AGAIN! Sorry for ranting and all. This probably just sounds like a dumb kid who probably over reacting, but wanted to see what you all thought. Thank you