Bleeding and severe abdominal cramps

I had to go to the E.R tonight due to having cramps and bleeding which was a bright red like my period. It was not light pink or spotting it was a heavy flow. I was prescribed a UTI and a threatened miscarriage. I got a normal ultrasound and a vaginal one and they said I have a sac but its too early for a heartbeat, etc. I also got a vaginal check, to check my cervix which looked good and closed. Is anyone else experiencing this or have experienced these symptoms? I have had 2 kids and never bled or cramped bad like this in the beginning of my pregnancy.