Pregnancy sings while breastfeeding?

I have an 8 month baby whom I breast feed and I didn’t get my period for the month of April-Just super light brown bleeding for like two days. I took a pregnancy test last Sunday which was negative but as of yesterday my breasts have been ridiculously sore and at first I thought I probably slept on them and have mastitis but I’m not so sure because I don’t have lumps on them or any other symptom besides sore boobs and cramping uterus feeling. Anyone else a similar experience and ended up being pregnant? I’m thinking about re-testing this weekend again