I am 3 days into my period, its lighter than usual and my basal body temp has not gone down. no chance of pregnancy. but i don't eat often. any ideas?

Sounds ok: There is nothing abnormal about having a light period. Many with heavy periods would happily trade places with you. It is not clear why you are checking basal body temperature during your menstrual cycle. This is not likely to yield any useful information and is not typically recommended. If you are concerned about an abnormal appetite consider seeing a primary care doctor or nutritionist.