Severe Abdominal Pain During Menstruation: Possible Endometriosis?

That sounds more like PCOS or endometriosis, based on timing i would wager PCOS. Ovarian cysts typically form because the egg follicles didn't burst to release the egg during ovulation and instead remain to swell with fluids and turn into a cyst so they most often start to form directly after ovulation even if the pain doesn't start right away. As they grow the pain gets worse so they present as an increasing amount of pain until it bursts, which is unbearably painful, and most often it drains in a way that just looks like spotting or even a period depending usually on the size of the cyst. If your menstrual cycle and the burst happen at the same time it can look like a really extreme period. Also as the cyst grows your bladder, colon, and even spine in some positions and with severe cases can press on it and make it significantly more painful causing pain while using the bathroom. They've been described to me as "worse than labor" by a mother of 3 and I most definitely believed her. However it's possible that you have endometriosis scarring that is mimicking it and iirc badly placed scarring and the accompanying hormonal imbalances can cause or worsen cysts, so it may be best to get checked for both if possible.

Before PCOS and birth control, my periods were terrible like that. Feel like my bits are gonna fall out, heavy flow, pain and bleeding during intimate moments, and inability to exist without ibuprofen on my period. My cramps would be so bad I couldn't eat for the first 2 days of my monthly. I got diagnosed with adenomyosis. Endometriosis is just as painful. Both conditions are some of the most painful ones to exist.