HIDA scan after an Endoscopic Ultrasound

I went in last week for an EUS to check for gallstones in the ducts as well as pancreas and liver.  I am still having nausea and some right-sided discomfort.  I've also been having some pretty bad diarrhea but after the EUS, was severely constipated for 6 days (pressure but no stools would come out).  My question is this:  I am scheduled to have a HIDA scan next week, which I pretty much insisted upon.  I was told this test would check for gallbladder FUNCTION which the EUS does not do.  If I have no stones, is it a waste of money and time to have this test?  I can pretty much put up with anything, but this nausea has been going on for 2 months.  Any advice would be appreciated.  Thanks you.