I've been on my menstrul for a month , and i'm not on birth control. what could the problem be?

Several issues: Menstrual irregularities can have several causes. Pregnancy is always a possiblity, especially if you are a young woman. Thyroid and other hormonal issues can cause irregular bleeding. Most commonly lack of regular ovulation. When a woman ovulates, the uterine lining recieves the signal to shed (through a rise in progesterone). If a woman does not ovulate, there is no progesterone, no signal.

Anovulation: It sounds as if you're experiencing anovulatory cycles. These are cycles in which the ovary fails to release an egg. This disrupts hormonal levels and makes the cycle abnormal.