Trying to stay positive.

AF is due tomorrow. No sign of her as I usually spot for 1-2 days before hand.  I've been testing for several days, even though I know I should have waited, and have gotten negatives with a couple super super faint positives. Have used a couple different kinds of tests. I have felt sick to my stomach for the past week every day to the point I feel like I'm going to be sick. My cervix is high and closed.  I just wish these tests would give me a decent positive if I am pregnant.  Is it possible that I am and just my hcg levels are still not high enough to pick up yet? I'm at 13 dpo today.