If the pain you are getting is on your upper right abdomen, just below your ribs, then that is most certainly due to IBS, I sometimes get pain there and my doctor told me that we have bowel up there and many people with IBS experience pain or discomfort in that area
The fact that you've said that your bowel habits change daily is also a good indicator that it's IBS, my bowels are never the same 2 days in a row.
Have you tried any of the medication that is available now for IBS? there are some pretty good ones now, also try altering your diet a bit to try and find out if there are any particular foods that make it worse, I can only eat tiny amounts of cheese, because cheese always upsets me and gives me the IBS cramps, so it is worth changing your diet about a bit.
I'm no doctor, but I would think that if it were anything more serious then something would have showed up in the tests you've had, and I know through experience, that IBS can make you feel pretty unwell and in a lot of discomfort sometimes hun