Abdominal Pain, Fullness, No Nausea Or Vomiting, Cholesterol Normal. History Of Mitral Valve Heart Murmur. Any Advice?

Question : Hi there, I am wondering if I should go back to my doctor. I have had upper right abdominal pain, just under the ribs, and a feeling of pressure or fullness that is keeping me up at night for at least 4 months now. I cannot tell if it is better or worse after eating or versus daytime or night-time; I think it is pretty consistently there. I have not had nausea or vomiting nor loose / bloody/strange stools etc. Antacids do not seem to help. (I did have one bout of stool that was very black, but otherwise has been normal, so maybe that was a fluke.) My doctor had some bloodwork done- my cholesterol and triglycerides were fine, bilrubin (spelling?) was normal and the other standard liver tests also came normal. (I forget the names but they were CGT, SOPT, APT /AST or AFT??) They were all fine and an ultrasound of the abdomen showed nothing unusual, no blockages, nothing enlarged, no gallstones visible, no growths or abnormalities. But the discomfort and pain is getting worse every day and wonder if i should be more proactive, in case it is something serious and I should get further tests. I don't really have a medical history except for a mitral valve heart murmur that is not a big deal and has been tested. Any advice on what else could it be and what tests I might get / need? ...Thanks a lot!