pregnancy fears

So I am 18 weeks 1 day and I only go to the doctors once a month and my last ultrasound was at 12 weeks (I have to go to 2 separate doctors because my insurance does not cover ultrasounds at my regular doctor) Anyways I get so nervous in the weeks between the next doctors visit like I'll go and hear the heartbeat and then I feel at ease but then 2 weeks later I'm getting all worried that something could be wrong. I hate this anxiety. Since I haven't had an ultrasound since 12 weeks and my next one is scheduled for the 25th I get so scared they are going to say something like oh the baby is not growing pr we dont hear heart beat anymore. I'm 18 weeks and plus size but I dont even feel a pregnancy bump yet and I feel no movement