What could be the cause??

What could cause someone to go from having very regular periods (went like clock work basically) with no cramps to suddenly having 2 irregular periods in a row with cramps? I'm getting seen soon but I just want some input on possible causes. I'm 25, 1 child via c section, ttc number 2 for about 3 years with no success. I've had a cyst in the past (probably about 6 years ago) that ruptured and haven't had another since, if that could possibly be the cause. TIA

EDIT: I've known people with miscarriages and I'm sure I'd be in a lot more pain and my periods would be super heavy not light if that was the cause. And the cramps I feel are very mild. Just little aches.