Bulges grom abdomen

When I bend a certain way, lean back far, or sit up from laying down, or even after eating when my stomach is full if I lean back, I get these strange bulges from my abdomen. and it leaves a dull pain afterwards. I have had a ultrasound of my abdomen around 2-3 months ago when i was having this extreme lower back pain and they didn't see anything. I thought it was phantom movement for a while from pregnancy but my daughter is 9 months now, and again it occurs when i move a certain way. I'm wondering if anyone would have any idea what it could be?? and if my back pain could have anything to do with it also??