I was on Trimethoprim daily from the age of 5-15, but infections got through. I had a run of infections at a similar age to you Debecca and again when I was early 20's. I then went on a daily antibiotic again but had to change every month to prevent developing resistance. It was a right pain and I've always felt 'wrong' (thrush, allergies etc) which I attribute to it. I came off them on my own accord a few years back and *touch wood* have been fine.
I'll go on a daily low dose again in third tri as I did last time, but ony cause UTI is so prevalent in late pregnancy. As medical conditions go it is managable, but I used to feel sorry for myself. Cystitis is grim but when it automatically turns into a kidney infection each time it really sucks. I missed quite a bit of school, and never even sat my GCSEs.
Still, I'm more grateful for my better health now. I have everything crossed for the little guy x