Contractions and bleeding?

Jenna • Mother of 1 bubbly little boy, expecting our little girl august 31st!
Last night I was having some spaced out contractions so I layed down to take a rest and when I woke up I went to the bathroom and there was bright red blood in my undies and when I wiped. I called my doctor who didn't seem worried and she said it was probably from my cervical check on Tuesday.  I wiped again and still bright red blood and a small clot so to the hospital I went. The bleeding stopped and the contractions stayed fairly spaced so we were sent home, but when asked why they said they weren't sure what caused it. Anyone else experience this?