Hi,
Welcome to the ehealthforum and I am glad to help you out
From the symptoms it looks like pancreatitis or choleystitis. Since the ultrasound has come out normal, so I suggest you to get a CT abdomen and pancreatic enzymes done. Pancreatitis may cause upper left abdominal pain which is worse when bending over or sitting. Pancreatic enzymes like serum amylase and lipase should be measured to rule out any pancreatic cause.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care.