Pregnant 5 months pp

Ok so I’m 5 months pp and just found out I’m pregnant. I felt like I had morning sickness tested that day and the next and negative. Woke up the next day and felt like I had morning sickness again so tested, and positive. I’m really early. Only 4 weeks. But I’m cramping really really badly . My question is, because I recently gave birth would that be why I felt morning sickness early on? And is that why I’m cramping so bad? Anyone with expirience with getting pregnant so soon after giving birth?