Hmm, your profile suggests you are 28, were you even having periods before you became diabetic?
I've been diabetic since 8 and have always had moderately irregular periods (plus a 3 year gap in my teams that in retrospect I think was caused by insufficient weight and/or insulin, though doctors pronounced me normal at the time). They only became reasonably regular after my second child, but then became so heavy that I got anaemia. (I have been on mirena since the age of 50 which eased things immeasurably).
Dr google says thyroid issues (much more common in T1s) can be a cause, so if you're looking for diabetic reasons I'd check your thyroid levels out. Otherwise if your BMI is on the lowish side you might want to increase your carbs and just be a little heavier?
Those are the only diabetic related reasons I can think of, though there may well be others. And of course, there are probably plenty of non diabetic possible cause.
Good luck.