From having had personally experiencing this.. I too had a gall bladder attacks. Same pain as you describe. I too was sent for the ultra sound. Came back Neg- (everything looked fine) I was then told it was acid reflux. Prescribed Nexium. It didn't help... I was pretty luck and had a good doctor that did believe me when I told him I was still having pain etc. He then sent me for an endoscopy. That came back visually good. A little inflammation, the biopsy showed H Pylori (I think everyone has that) Anyway, 6 months later still no better just getting worse... very worse. Didn't matter what I ate or did. Got so sick and became Jaundice. (So what happened ended up with 2 stones that traveled down the bile duct. One got stuck and well, surgery it was.. So even though Ultra sounds are good. They are not 100%. When they do the ultra sound, it looks for shadows, if the stones are sitting just right, your test will come back Neg- (just as mine had)
Now it is possible that it's not gall bladder related. It could be a stomach ulcer... or bad acid reflux. But with the info you have given me.. I would say it's the gall bladder. Hopefully you have a good doctor and you can talk to him, let him know that the pain is still there. You may even want to go to a specialist if you can.
You can try eating a really bland diet for a few days to see if that will help. No fatty foods, spicy foods, cola. Try to keep it jello, crackers, plain toast, (Turkey from the deli always agreed with me)
I hope this helps and gives you another point of view.. If you need anything else or have any other questions, please feel free to ask.
Otherwise good luck and DO keep me posted OK? If you found this helpful, please hit the accept button and leave me feedback as I will do the same.