Ovaries form cysts each month during the ovulatory phase, roughly 2 wks from period to ovulation. One cyst ultimately grows the largest (wins the race) and that is the cyst that releases the egg. As you ovulate, the cyst bursts open, the egg shoots out and the fluid leaks out. Some women, myself included, are often exquisitely sensitive to the fluid. It really irritates the heck out of the abdominal tissues for me. I often get a lot of pain with ovulation. Sometimes it's on one side, sometimes on both sides, sometimes the front only, sometimes it wraps around to my back.
Google mittleschmirz (German for middle pain, and I hope I spelled that right). Sometimes, middle pain occurs ONLY at the moment of ovulation, other times, it last for a few days (as it does for me). That's usually for those really sensitive to the fluid.
I've been to my gyn a few times when the pain is there to get u/s. They usually see that it has burst in the recent past (day), and can see some fluid spilling in the area.
I don't get bad pain every month. It varies. Some months I don't even know I've ovulated, other months, it bugs me for a few days. Sometimes, it's bad enough all I want to do is sit and curl up into a ball. (Mind you, I can't do that, but I sure as heck want to! Thank goodness for my dh - he takes on a lot of chores for me when I need him to.)
Last time, I said something to my gyn about the cysts sometimes having more prostaglandins than other months. My gyn just kinda nodded her head in agreement, but didn't really say, "Why, yes, they do vary!" Prostaglandins act at pain receptors and can cause really bad cramping. I know semen contains prostaglandins (don't ask, it's an IVF thing), so it seems likely to me that ovulatory fluid could have them, too.
You can also have a persistent ovarian cyst. Usually this happens when, for one month, the pre-ovulatory cyst grows, but then it never bursts in actual ovulation. Instead, it hangs around for a few extra weeks, sometimes months. This can easily happen during times of high stress (like getting a dx of CML). Stress can throw off the hormone cascade that must happen for ovulation to occur.
Lastly, I will say that I noticed much more painful ovulation the first few months following my diagnosis. I half wonder if the stress doesn't somehow increase prostaglandin production during the ovulatory phase.