I haven't had my period for about 3 cycles. i am overweight and have recently gone off my antidepressants, welbutrin.

Several causes: Absence of periods has several causes. The medication change could definitely be a factor, as can various kinds of stress, but you definitely should do at least a home pregnancy test (perhaps already done?) & ask Dr @ doing a thyroid blood test & perhaps a few others to help determine the cause. Decreasing calorie intake & increasing exercise gradually to lose weight may also help restore periods