Bleeding at 10 weeks

I have bleeding this morning that turn from pink to red It wasn't heavy but I'm 10 weeks pregnant and it freaked me out so I went to the hospital. They did HCG level tests which were normal pelvic exam that was normal and understand they said the babies heartbeat was normal growth was normal and ultrasound was normal. They said it was normal bleeding. I haven't had any bleeding during the first trimester before today so I'm a little confused what can cause normal bleeding this late into the first trimester