Pregnant ??

So I took a pregnancy test today around 1pm and it immediately turned positive. I have had dark brown spotting over the last few days so I went to the doctor to make sure everything was okay. Their urine test was negative but the blood test was positive (barely at 29) and the ultrasound didn’t show anything in my uterus yet. My last period was July 18th but I tend to range anywhere from 30-41 days. What are your thoughts?