Breastfeeding and missed period.

My daughter is 7 months old. I started getting my regular periods . I had a few months. Around November 10th should had been my next one. I've had some spotting then. I keep thinking I'm pregnant but I've taken two test and there both negative. I even have nausea come and go. Im wondering is this all in my head. has anyone experience this before and became pregnant. let me add if I am great. If I'm not o well.