8 months pp am I pregnant again!?

I had my period June 19-22 and then I started bleeding/ spotting again July 6-9 but it was pretty light and would start and stop. I’m not sure what’s going on. I’m now experiencing intense lower back pain, tiredness, and have a dull ache in my lower abdomen. I took a pregnancy test yesterday and it’s negative, possibly something there but hardly. I’m so confused. I’ve been with the same man sexually and don’t have any signs of infection. I had my daughter 8 months ago, I’m on birth control (mini pill because I’m breastfeeding) and we are not trying for anymore babies. I’ll post a picture of the test. Tell me what you think?