Bloody discharge AGAIN!

Does anyone know what could be causing this? I'm 33 weeks pregnant and over the last week this has happened 3 times. It's red/pink blood mixed in with discharge. I called the midwife unit the first time it happened and she said if I have no pain then there's no need to come up. I woke up 2 nights ago with extreme back pain I was in tears, and the only other pain I've been having is pelvic pain/pressure and shooting pains down low. Is this normal or should I get checked seeing as this just keeps on happening? I also had to take antibiotics for chlamydia 3 days ago. Could this have anything to do with it?