17 weeks pregnant, a lot of cramps and back pain in the lower left, very dizzy and nauseated as well as very weak, I had an UTI and took pills at 12 wks?

Go back to doctor. You may have recurrence of UTI or it may have become chronic. Or something else may be going on. In any event the best thing to do is to allow a doctor who knows you well to examine you and test you to insure your health and the welfare of your future great baby. Be well.