Fighting with my brain

I'm spending so much time fighting with myself...

My full-term son died at 3 days old last year. I'm 12w exactly today on my first pregnancy after him, and my mind won't be optimistic about anything. 3 weeks ago, we had a healthy dating scan, everything looked fine. ...But by the next day, those reassurances dried up. I spend every day thinking that I've had a missed miscarriage, that I'm not actually pregnant anymore, that when we go in to see my OB next week, he won't be able to find a heartbeat with a doppler, either. (I've got one from my first pregnancy, and could hear my son's clearly after 11 weeks; can't find anything, now.)

I haven't told my family, besides my sister who's a doula, because I just don't feel like there's anything to celebrate. It's too early to feel movement, and even though I ought to be able to pick up a heartbeat by now, I can't. How do I stop spending every day *knowing* that my pregnancy has already ended, **without actually knowing that at all**? My brain hates me and won't let me feel any joy; just waiting impatiently for the harsh truth to become real. How can I reassure myself that everything is fine when there are no ways to find reassurance?