scared and spotting

I woke up this morning, headed to the bathroom, no blood on panties but I wiped three times to see like pink staining/watery on the TP. There was this one little glob that looked dark red, like a clot, but was smaller than the size of a pencil eraser head.

I called the doc on call, he said if no cramping then try not to worry. He said if bleeding picks up or I start cramping, to head into the ER to be assessed. He said it could be a subchorinic bleed or implanatation spotting. I said, at 8 weeks? He said that often in 6-7 week range, the baby burrows in a little more as that placenta is forming and can cause some light bleeding. Anyone ever heard of this?

He asked if we had an U/S and I said yes, and with a heartbeat, and that was reassuring because it ruled out other stuff.

I'm still very concerned...