What Causes Frequent Headaches, Nausea And Dizziness?

im a female, 17 years old and i have frequent headaches, nausea, dizziness for the past week. i feel like my body temperature is hot but its normal. i take dieting pills that decreases my appetite. i have been sexually active (unprotected) and just had my period 2 weeks ago. im irregular. what could this be?