Irregular cycle for 11 years, last 4 months have been regular

Hi! I have had my period now for 11ish years. I got it when i was around 9 or 10 and i am now 21. For all of my menstruating life lol, i have been irregular. I don't have PCOS or hormone imbalances. I was on birth control for maybe 5 of those years and my cycle was still not regular. For my last 4 cycles, I have been regular! Every 32-33 days i get my period. I haven't done anything differently or changed any medications. Has this happened to anyone before? If so, did you ever find out the cause? Thank you!!