I m always late one or two months.. what could be the reason?

See a physician: Some patients have irregular cycles. Pregnancy should always be excluded. There are medications you can take to help get it under control. See your gynecologist for consultation.

Menses irregular: You may not have begun ovulating regularly yet, there may be some hormonal imbalance, you may be pregnant and losing the fetus without knowing. Go and discuss with a gynecologist and they can give you a more specific answer.