I Am 18 Days Late On My Period, I Am

I am 18 days late on my period, I am usually a month to month gal, if i am ever late on my period it'll be by the most 3 to 4 days max. Never this late. I thought I was spotting this morning but it didn't happen again anymore so it might have been a mistake. I have had cramping for the last 3 days, I am loosing a lot of hair, my nipples are really sensitive. I have taken 4 pregnancy test and one blood test and my HCG level was 1. I have convinced myself that I am pregnant. Could I be pregnant?