How to stay positive during the first trimester?

I'll have my third ultrasound at 8.5 weeks tomorrow. So far both babies have grown right on track, have excellent heartbeats (159 and 162 at my 7.5 wk ultrasound), and are measuring a few days ahead of schedule. I had some brown spotting a few days ago but the OB says that the progesterone suppositories cause that and I shouldn't worry about it unless it's red and I have pain along with it. I haven't had morning sickness for two days and though that's not abnormal for me, every time I have a symptom subside or go away I get very nervous. So needless to say I am on pins and needles about this ultrasound tomorrow. I'm finding it very hard to stay positive and not worry.