Moveable lump in stomach , please help!!!!

[soccergrl]

Let me start off by saying that I have had an inguanal hernia repair two years ago. Since the surgery I have noticed a large moveable lump which I can feel mostly when I'm laying down. It pulses, like a heartbeat, but I can only feel it from the inside not the outside. It starts on the left side of my stomach, but when I push down it, it moves all the way to the right side of my stomach. It passes under my belly button, and is not painful but very VERY uncomfortable. I've visited my doctor before but he could not feel it even though I very well could, but the other day I went again and he felt a "weakining in the wall" and that I should go to the surgeron who did my last hernia repair. When I went to my appointment with the surgeron , not even he could find it. Does anybody have any idea what this could be or has anyone had anything similar to this ? It's really very uncomfortable =\