We've been ttc for over 18 months (we already have existing children, no fertility problems before), unsuccessfully.
I have a 28 day cycle, but (regular as clockwork) get stomach cramps, both sides, and lower back pain (without bleeding) on day 21, then some spotting a few days later and then AF starts, which is painful, but bearable and no different than has always been.
I also get some pain (lower abdominal cramps) after sex, and milder abdominal pain sporadically, on-and-off. I think it is getting a little worse.