Ruptured ovarian cyst

So, this morning I woke up in excruciating pain. I fear an ectopic pregnancy, but I was actually an ovarian cyst rupture. I’m googling but only seeing that it can happen to anyone. But... this particular cyst they have been watching for a long time. Like years. Anyone know what would cause a cyst like that to rupture? Didn’t think to ask the ER doc. And I will wait to call my obgyn until Monday.

*this is my first month on femara/letrozole

*two months ago I had an HSG procedure done.

*been TTC for 8 months. Started my period two days ago.

Thanks for any info!!