Possible twins!! What do you think?

Leahjo
Went for our second checkup yesterday and heard babys heartbeat for the first time. There where two heartbeats!! and my uterus is measuring 18 weeks at only 13 weeks along. Doctor said no guarantee but very likely twins. Waiting to go for an early ultrasound!! What where your early twin symptoms? Do you think it's twins? I'm going crazy wondering!!