Dark/black stools can be an indication of blood or of severe constapation. Stomach pains and nuesia can also be a sign of constapation, but also of many other things.
I have a friend with Polycystic Ovarian syndrome and it has never effected her bowels.
Whatever is causing you problems, it doesn’t sound very fun. I would see a doctor asap - as it could start effecting your weight and lifestyle. Sorry this isn’t overly useful! I wish you luck in getting it sorted! - written 4 months, 3 weeks ago