No appetite, getting full fast

Hi, I'm 14, I'm on my period if that has any importance, and the problem is that I never have any sort of appetite lately and when I do I'll try to eat something and get full within only 3-4 bites. I wouldn't exactly say I'm a shy eater either, I used to always be hungry and eating to eat. In fact I still want to eat even now, but I just can't seem to get my body to want it. This has been going on for a little Over a month, So can someone help? Thanks