Hi I'm A 21 Year Old Female. I Have A

Hi I'm a 21 year old female. I have a almost 2 year old daughter. After having her by c-section I got an iud. Recently my periods have been really sporadic and light. I'm having pains in my back and ribs and movement in my stomache. I have taken home pregnancy tests and they come back negative. It feels like kicking in my left side then moved to up under my ribs. Any ideas what this could possible be? Yes I am sexually active.