Heavy bleed and passing clot

I was shopping at hobby lobby with my mom and son when suddenly I felt a gush of fluid, this is my third pregnancy and all have been high risk since I lost the first one due to incompetent cervix. I go to the bathroom see all the blood and what looked like tissue. We went straight to the ER and after running lab, ultrasound and pelvic they could not find any source for the bleeding. I am 13 weeks today. They gave me the progesterone shot as I had those with my second pregnancy after I was spotting. The bleeding Stopped quickly after the shot was given. I’m not passing some clots but it is visibly old like it was sitting in my uterus before expelling if that makes sense, along with a small amount of brown old blood. I’m supposed to have the cerclage placed the week of April 15th. Any advice? Any thoughts or possible ideals? I’m used to the crazy ups and downs with my pregnancies but I was never prepared for this and thinking I was going to lose my baby in the hobby lobby bathroom. Ps I was in no pain the entire time.