Stomach pressure/pain when laying on back?

[CallMeBlondie]

When i'm laying on my side, sitting/standing up etc. I'm pretty much fine, it's only when I lay on my back that it feels like my stomach is heavy and I can feel it pulsing and whatnot. It's pretty strong when I press down too. It also tends to feel shaky/jittery off and on all day. I've been having abdominal aneurysm fears for months now (and I'm only 22  , 5'1 and around 110 lbs normally) but I've only noticed all this going on since my anxiety kicked in badly early last year so I don't know if it could be from nerves, possible IBS? (I'm not familiar with a ton of the symptoms of it) or what. It's just odd. I have a doc appt on Wednesday so I think I'll bring it up then but I was just wondering if anyone else has these symptoms too.