What causes bladder infections and what are things I could do/take regularly to prevent them? I just…

What causes bladder infections and what are things I could do/take regularly to prevent them? I just had the worst one of my life that was so bad it started my contractions and I am only 32 weeks! I've been on antibiotics the last couple days but the pain is slowly coming back and I have to stop it; I cannot go through that again! What am I doing wrong?!