I have been feeling nauseated with headches and no apitite. i had sex a month ago but i'm on birth control. i also have low energy levels.

Go see your doctor: Many reasons for what you've described, too many to give more than general ideas. 1st, you might just be sick w/virus. 2nd, you could be pregnant if birth control not used as directed. 3rd, you could be anemic or have hypothyroidism. These last two would not explain nausea ; headaches but could cause low energy. Bottom line, go see your family doc for complete evaluation.