Breastfeeding and pregnancy

I wanna know is it possible for me to get pregnant with my second child. I had my baby girl 4/6/2018. I breastfeed her. I got a depo shot when she was 6 weeks. But I haven’t gotten another one shot. Thursday- Saturday. I had a onespot each 3 days. The blood of the spotting was dark brown pinkish but when I took pregnancy test Sunday and Tuesday they both came out negative.