If you are not on birth control, it could be perfectly normal. I went off birth control for close to a year and during that time I went like 2 months without having one, bled for almost a month straight, then had a couple normal periods....some light, some heavy.

There are so many things that can affect your period if you are not on some kind of hormonal meds. Stress, lack of sleep, diet changes etc... If you are curious about it or want more answers, set up an appt. with your OBGYN and she can help you out. Most likely, she can give you birth control to even you out.