can stress cause pregnancy symptoms??

Anyone else ever worry so much about pregnancy that they actually felt symptoms. 
I have had negative hpts and periods still. 
I have literally been thinking I could be pregnant for 5 months now and can't get it off my mind and I feel like maybe I'm giving myself symptoms? 
Is this even possible?? 
I had an ultrasound but it would have been early 6-7 weeks and they didn't mention anything about be pregnant in the report. 
Could I be stressing so bad that I'm giving myself symptoms??