Can anyone tell me what's going on with me? TTC

I got these two positive tests on the day of my expected period but the next day I started my period which I thought could have been a miscarriage but I went to the DR & they ran a quantitive blood test as well as an ultrasound & both tests came back negative. Now a week later after I have already brushed off the idea that I may be pregnant, I realize that I am lactating again. I haven't retested but can anyone tell me if they've had a similar situation? I am 6 & 1/2 months postpartum & haven't breastfeed in about 4 months.