It sounds like hemoroids more than anything IBS related, though at times my IBS-D has been so bad that I could not sit down because the IBS-D actually caused awful hemoroid flare-ups. You may want to be sure you are going to a Board Certified Gastroenterologist. Your choice of doctor is very important if you want a very qualified medical opinion on digestive issues. Until then, you could try a hemoroid cream that has an analgesic agent (to numb the affected area). You may want to pick up some "Always Ultra Thin Overnight Feminine Pads" until this problem is solved. If you are a male, the clerk will assume it's for your wife. The pads will help when you "almost" make it to the bathroom, saving you tons of embarrassing moments (trust me).
If you have IBS, you can get some minor anal bleeding or even anal fissures. IBS can be quite painful, no matter which way it tends to be. I would be very careful about NSAID pain killers, because they can cause more bleeding. My problems tend toward IBS-C, but if you're tending toward IBS-D, you really need to keep working on the issue. Be mindful about how much magnesium you take in, because too much magnesium can and does cause diarrhea. You still need a minimal amount, in order to stay healthy, but magnesium can actually cause problems for people who already deal with diarrhea. I'm sure you use Immodium and other anti-diarrheal medicines. Has your doctor prescribed antispasmodic medications. A good one to try is Bentyl. The reason I say this is because it does slow the colon down. That's why my doctor wants me to use it as little as possible. It is sedating, which is a major drawback, but I use it for IBS-C myself, because it will stop the pain from the colon spasms. The generic is Dicyclomine. There are other antispasmodics out there, but this is the one I use with success. I tried Hyocyamine before and it didn't do anything for me at all. I think Bentyl or Hyocyamine would be worth trying for you. I had more success with Bentyl.