Severe Stomach Pain and Discomfort

Hi there, been experiencing severe pain and discomfort in right side of my stomach and right upper back quadrant, this is always worse after eating or when lying down or sitting back relaxed. I now also experience same pain and discomfort in left upper quadrant in my stomach area under my ribs. The doctor was convinced I had gallstones, classic symptoms apparently but, after an ultrasound on Monday I’m told there is no gallstones there. I’m very worried it could be something more serious but I just need to wait and see what the doctor says and suggests next to try and diagnose the cause. Just wondering if anyone has had similar symptoms and how long it took to feel better or find out what was causing it? I keep well normally, am a bit overweight and only drink socially but since consulting with the doctor I have been on a low fat diet and lost just over half a stone and have not drank alcohol in nearly 3 weeks, the changes don’t seem to have helped with the pain although I know the changes will help in the long run. Thanks :)