What could this be

I have a three yr old so I know what it feels like to feel a baby kick ... My periods are irregular and for the past week I've felt like a baby kicking in my stomach on the left side of my navel... I can actually see it when it happens what could this be I've takin pregnancy test after test last couple months n all negative n my period only lasted for two days this month... Does anyone know what this is or had this happen?