I don't really have any insight other than our bodies are strange strange things.

I used to be like clock work and then i hit 17 and my AF became very irregular, heavier than normal lasting longer than normal and i started to get period pain where as before i haven't.. for 3 years i was told it was "normal" when infact i had PCOS. Not saying you do but its just so hard to keep track of why our bodies do what they do.

Have you been stressed lately, lost weight? gained weight? changed your diet? gone on or off the pill recently?. I'm just guessing but these things can have an affect on our bodies.

If your concerned you should speak to your doctor.