Pregnancy? Nigra a sign of pregnancy?

I know I have been asking this a lot of times but everytime I notice a change in my body  I panic. Last intercourse was on 9sept. Did a usg pelvis and beta HCG on 9oct that came 0.4 Had periods (bright red with clots) on 22sept, 3rd Nov, 4th dec, but they stopped after 2-3 days. Again did a usg pelvis and beta HCG on 3rd Dec that came 0.2 and endometrial thickness was 6.8mm with bulky ovaries. Uterus is anteverted. The report said that there is no focal mass lesion in the uterus. But I'm noticing a line like linea nigra below my umbilicus. I am not sure that it is there from earlier or not and I'm also noticing some growth in my belly. Am I pregnant ? Is linea nigra a sign of pregnancy? I'm attaching the pelvic usg scan here . Please help. Thank you