Hi! How are you? Well I know, probably a lil worried. But you shouldn't be. I had a low lying placenta with my second pregnancy. My doctor called it placenta previa. Pretty much my placenta was covering the opening to my cervix. Luckily, I was only about 35ish weeks when they found out, and by the time I was ready to deliver, as my belly grew, the placenta moved up. Your only 18 weeks along, so that should give it plenty of time to move as you grow. Hope I helped at least a lil bit.
When are u due? And congratulations!