What Does Fluttering Feeling Like Bubbles In Uterus Mean?

I have a feeling in my uterus on the left side like I'm early in a pregnancy (i have 2 kids and this is the same feeling). It feels like bubbles and happens mostly in the morning for the past 3 days and I can feel it more when I'm sitting. It's always in the same spot. No pain but REALLY irritating. What is this feeling???