Iud and sometimes I feel movememnt

so I have had my iud in since 6 weeks pp so it's been about 4 months since I had it inserted. within the last month I have started to feel movement in my abdomen however I took a test about a week ago and it was negative. I am still having my periods but they are abnormally light and it's more of like bloody discharge than actually spotting. my husband thinks I'm crazy. I think I'm just trying to distract myself from other issues like my weight. but I can clearly see my belly move to what I'm assuming is my heart beat and I can feel movement. It's usually early morning or at night. I don't know what's going on. my strings are still in place though. I do experience a small cramp that is sometimes on my right side ovary are but sometimes on the left. any ideas what's going on?