I don't know if this question is still needing an answer, since it's a year and a half old.... but it sounds a whole lot like what I've dealt with. Finally, now that the discomfort has gotten much worse, after about a decade of going to various doctors who were very dismissive, and searching online to no avail, I finally found a doctor who knew immediately what it was - my gallbladder. Just did a hida scan, and they found that it is barely functional now. Perhaps if they would've checked my gallbladder years ago when the damage was just starting, minor treatments possibly could've been used. Go in for surgery in a couple weeks to get it removed asap.
Of course, it could just be a cyst. However, you should get your gallbladder checked just in case... you really want to find out before you need surgery or before it ruptures.