Another typical thing is a parasitic infection like pinworms/threadworms. They are very common. They bite into the gut wall when they grow or mate, and can lead to appendicitis on the long term. the pain is usually right or left or even underneath the belly button, and feels like a pinch with a needle or, if more severe, a hot knife.
Get a scotch tape test done, best in the week after full moon (they are more active then).
Good luck.
Most people with appendicitis have severe pain worse than what we usually get with IBS. Although, as you must know by now, you can get severe enough pain from IBS to even keep you from being able to walk. You can get IBS pain anywhere in the abdomen, and the left side where the descending colon is, is typically the most common area of pain. I have had the pain in the area you are talking about. Two things can be going on that are more likely, if the doctor is sure it's not the appendix. One thing is that it could be the gallbladder. This doesn't mean you need to have surgery, though. Not all gallbladder issues are related to gall stones. I get pain in the area you're talking about at times from the IBS, and the tests were all negative for gall stones. So, one theory is that if it's not the colon itself that it could actually be the gallbladder having spasms. And, this would actually be related to the IBS. The other theory is that it's the colon itself. No one can know for sure without sufficient cause to need to go in and do surgery. And, no one is touching me for surgery until it is absolutely necessary! I suspect that it's either your colon on the right side of your abdomen or your gallbladder. One or the other could be having spasms causing the pain you're having.
One way to figure out if this is the case is to try a prescription anti-spasmodic medication. If the anti-spasmodic medication reduces the pain, then the pain is related to your IBS, whether it's the colon on the right side or the gallbladder having the spasms. Both are part of the digestive system.