extreme back pain sign of labor?

I'm 27 weeks, I had sex this morning and afterwards lost a lot of blood (about 1/3 C) I went to the hospital, and they looked at me and asked me questions, they told me my cervix is still closed, and it doesn't look like active bleeding so they let me go home. However the doctor asked me if I've been experiencing any back pain, and I heard of back pain being an early labor symptom. And I'm having bad back pain right now, I didn't before so I said no, but for the past few hours it's been really bad, I don't know if this is hurting because of strain, or because of labor. I'm really scared because of the incident this morning and this during the same day. 
My ribs also feel really tight, and like there's a lot of pressure happening on them, I don't know if that would have anything to do with anything, but today is the first time I've ever experienced that as well. I can still feel the baby moving around though, I heard that you don't during labor. Also my belly has felt weird all day, like constant pressure. 
Should I be worried?