20 weeks and bleeding with 1 clot!

I saw bright red, went to the ER. Doctors ruled out placenta or cervix. Baby is fine and I am fine. Discharged from hospital I still have a light, brown spotting but I assuming old blood. I am not feeling any pain just concerned because it was red blood. Also, did not have intercourse during that time so hey also ruled out that. ER DR didn't say much and give an explaination as to why. Has this happened to anyone else?  Please help!