It very well could be your gallbladder. Do not eat high fat food ! This is the worst thing for it and can prolong your nausea. Eat low fat food every day until this is tested further. I know you are losing weight but try small low fat meals several times a day and this may help a bit.
The HIDA scan was done with CCK... It didn't make me sick at all, and I was expecting it to... My doctor still suspects it could be my gallbladder, she said she has seen it happen before that for whatever reason the gallbladder didn't act up during the test.. She suggested that when and if the pain happens again to go to the ER so maybe they can do the scan during the attack. I was having the pain pretty frequently for awhile, however it hasn't happened in a month or so... Right now my main complaint is nausea. It almost seems to 'flare' ill be good for a week or so then all of a sudden it hits and Im sick for days. The weight loss is also concerning. I don't eat a whole lot for fear of getting sick but when I do eat I try to make it count by eating very high fat food.
Did the HIDA scan include CCK infraction? The CCK was the part of the test that mimicked my pain and nausea, and did so about 5 times over the course of 30 minutes. Due to pain in the center of my abdomen and this CCK replicating my symptoms, I had my gallbladder removed. The pain in my abdomen is gone although I still have persistent nausea (different than before) and some continuing abdomen pain, but the gall bladder was not functioning properly and contributed to my health issue.
Good luck to you!