IBS is often the diagnosis they give to celiacs or those with non-celiac gluten sensitivity (NCGS) before they have figured out the cause of the pain. Someone around here used to joke that IBS is a doctor's acronym for "I Be Stumped".
Do you know the ranges for those celiac tests you had run? The tTG IgG, DGP IgA, and DGP IgG tests look negative but if your range is very small (like 0-1) it could be positive.
I would advise you, if you are satisfied all of your celiac testing is done, to try the gluten-free diet for a few months. You could have NCGS, which is evrey bit as nasty as celiac disease but does not include intestinal damage, so you may need to eat gluten-free. Celiacs, and those with NCGS, do not always (or even often) feel better immediately after going gluten-free. Some symptoms can take months or years to resolve so giving the gluten-free diet a trial of around 6 months is often the only way to go. Make sure you are strictly gluten-free. Trace amounts every few weeks is often enough to set people back and hamper their recovery.
Best wishes to you. I hope going gluten-free long term will help you and you'll begin to feel better soon.