What causes irregular periods?

I have a question about my period, but I will give background info first. I am 29 years old, and I have a six-year-old. Before getting pregnant, my periods were really irregular. I would get them monthly but just never knew when. I had my daughter and got on Mirena birth control. I actually loved it in the beginning. But at the beginning of year 5, I started having some mental health issues (not related to birth control, or at least my doctor didn’t think so, and I do have a history of it in the past) and just wanted to remove it and I did. I got my period a month later and have been super regular ever since for a whole year, which I really enjoyed. Now, my period has been super irregular for the last 4 or 5 months. From coming on a little early to skipping almost a whole month, and most recently, I’ve had a second period for the month of April. One in the first week and then the last week. And surprise! It’s 10+ days later, and I’m still bleeding. It hasn’t been bad at all other than some unusual cramping (I rarely cramp, just bloat, get acne, moody and sore boobs), but this has never happened to me before. I have an appointment Friday, but I’d like to see some of you guys’ responses. So my question is, if this has happened to you, what was the issue? Was there an issue found? Was it corrected? etc…I would like to hear some of your experiences. Thank you.