bleeding at 15 weeks

So, I woke up Sunday morning and discovered that my underwear was soaked in blood. Of course I begin to freak out. I called my wife in as calmly as I could, as I didn't want to freak out our 4 year old. She was also freaking out. I called my midwife who suggested I call her back-up on call midwife at the hospital. It took over an hour and me calling twice before I got a call back. She was super nice, but more relaxed about the whole thing than I was feeling. Wifey dropped DS off with a friend for a prearranged play date and met me at the hospital. Baby had a strong heartbeat and she did an exam then sent us to radiology for an ultrasound. It being Sunday, everything was extra complicated. The ultrasound showed baby growing well and no obvious reason for the bleeding.