30weeks Blood Clot?!?

Just left my OB office for my weekly checkup (due to being high-risk). I've been spotting since about 26 weeks, to the point where I wear a pad every day. Last Tuesday, he checked on baby and hooked me up to a contraction machine to make sure I wasn't experiencing labor-- everything looked fine. Since I'm still spotting, the doctor decided to do a transvaginal ultrasound today to see what was going on--said that I have a blood clot in my cervix! Said that it will continue to "come out" little by little, hence the spotting. He kind of brushed it off--but I'm totally freaking out! I have no idea what could have caused it and he didn't give any explanation...😩😩😩
Has anyone had this and can offer insight?!