Rainbow baby

I'm having such a hard time being positive even though I'm 15 1/2 weeks. At my 12 week apt they were unable to find the heartbeat so did a quick ultrasound and said the heartbeat was there and everything looked fine but they didn't tell me what it actually was. I didn't think to ask... And I keep on thinking there was something in the Drs expression but that can totally be paranoia. I keep running scenarios through my mind of the gazillion ways this pregnancy could end. I just want to enjoy it and feel like at the end I'm going to be holding/getting to know a perfectly healthy son or daughter. :( my brain feels unfixable though. :(