Just get yourself more thoroughly checked by ob-gyn.

I've had uneven periods for different times of my life and a certain part due to lots of cycling (triple the amount of mileage compared to now), have been slightly underweight (not now though) and stress.

ButI never got painful cramps during my periods. Just normal periods.

I'm in perimenopause....I haven't had a period for past 6 months but am in my early 50's.