What could cause extreme hunger?

These last few days, I keep getting so hungry. I'll eat and feel full and then a few hours later I feel like I haven't eaten in days. I wake up in the morning more hungry than I've ever been. My stomach starts to hurt, I feel light headed, and just all around not well.

I haven't been eating any less than usual. If anything, I've started eating more because I've been so hungry. I have not changed the type of food I'm eating (other than trying to eat more filling and nourishing foods since this started), I haven't started taking any new medications or vitamins. Literally nothing has changed.