Depo shot

Recently, it’s been about two months of being on depo. I’ve been spotting for two weeks, except it’s heavier than spotting. The spotting changes color, from deep red to brown, to lighter red. I still have to use a tampon. I’ve been having slight “cramping”. I’ve also felt a little heart burn I guess? Almost like cramping in my heart😂 I’m not sure if I’m just freaking myself out thinking that I might be pregnant. But I just wanted to know if this was normal?