I Am 18 Weeks Pregnant And Have Had A Bladder

I am 18 weeks pregnant and have had a bladder infection with various strains of bacteria since 9 weeks. The first two strains were taken care of with antibiotics but the second strain did not go away with treatment; klebsiella pneuomania. They want me to now take septra ds antibiotic but it is a category D, which I do not want to do. Any suggestions? I haven't had a bladder infection for 15 years nor did I have one with my first pregnancy, what's up?