bleeding

I'm 20 years old and I have an 8month old daughter. I had unprotect sex and now for the week I have been bleeding on and off and it not heavy or anything. its light. it goes from bright red to light. I'm scared. what shall I do. I have told my boyfriend about this, should I tell him about it. my back been sore and I have had really bad cramps fro about to 2 days. my breast r really tender and sore. I'm thinking about ringing my gps in the morning!! has anyone expencines this. many thanks

(sorry about spelling mistakes)