Blood Clot

We went for our first sonogram Tuesday and were 7.5 weeks. The baby looked good. Heartbeat was 137. The Dr. Called today and said that there's a 2mm sac of blood by the placenta or on the placenta. He said not to be worried right now and that I will need to follow up with another sonogram in 2-3 weeks. Has anyone been through this? I know I shouldn't have looked online because now I'm upset.