Today I'm 6 weeks and terrified

Hillary • 31 year old Registered Nurse, mom two girls aged 10 and 7. Celebrated our 11 year anniversary this year! Expecting #3 December '16!
I'm suddenly not feeling pregnant today and it is terrifying me. I had a MMC in December and had no idea anything was wrong until I had my 8 week US. The baby stopped growing at about 6 weeks 3 days. I don't have my first ultrasound until May 6th and I'm having a hard time worrying today.