A bulge in the center of the abdomen is frequently due to a ventral hernia, but if the ultrasound looked at the bulge and was normal, then this bulge would be more related to a weakness along muscles of the abdominal wall, rather than a true hernia, although over time, the weakness can evolve into a hernia.
If there is no hernia, the bulge would not be causing the other symptoms that you are experiencing. An enlarged liver with elevated liver enzymes can cause a variety of abdominal symptoms, although it will more often cause upper abdominal symptoms.
If the cause of the liver enlargement is unknown, then further evaluation of the liver would be appropriate, and it may be necessary to be seen by a Gastroenterologist. Another option would be a trial of a interventions to try to relieve the symptoms that you are having. There are several home interventions that can be considered. It may help to take probiotic supplements. I may help to increase the amount of fiber intake, either by high-fiber foods or fiber supplements. For the gas pains, it may help to use simethicone or activated charcoal.
However, if the ultrasound did not show the bulge to be a hernia, there is no reason to suspect that the bulge is causing your other symptoms.
If I can provide any additional information, please let me know.