I keep feeling pregnant again...

I have a 5 month old baby boy who I love so so much, but since I was a couple months postpartum I keep feeling like I'm pregnant again. And I really don't want to be right now. I want to give my some all my attention for at least a few years, but I keep feeling bloated/ crampy, sometimes nauseous, and sometimes swear I feel little flutters (phantom kicks?). I've taken 2 pregnancy tests and both were negative, but I keep worrying. I'm breastfeeding and on the mini pill and we usually always use a condom just in case. But I can't shake the feeling and I'm not sure if it's just my body freaking out from not being pregnant anymore or the tests are giving me false negatives. Any other postpartum mommies feel this way?