the past few days I have had really bad back pain and pelvic pain ( I move and its excruciating) .…

the past few days I have had really bad back pain and pelvic pain ( I move and its excruciating) . my left side today has started to hurt now!!!! I'm feeling very tired and I've had five kiddos and pregnancy hasn't ever made me tired. ugh ladies tell me your opinions of what you think is going one. I've been taking a new antibiotic ( had a uti and doctor switched me to this because she said I had the strep b bacteria ) but I don't think that would cause all this