I have been there!
Remember crying out of desperation after having UTI's followed by yeast infections from the antibiotic treatments. Endless cycle.
My last UTI was while TTC our dd. Before that I had UTI's almost once a month for 4 years. I tried everything and saw a urologist who prescribed a low dose antibiotic to be taken every day.
Adina posted a great list. I'll add to that...
Drink *at least* a gallon of water a day. It may seem difficult at first but soon you'll be addicted. If you aren't using the bathroom every 30-60 minutes, step up the water. Your urine should look almost clear.
Try to lower your stress in any way possible. Stress lowers your resistance to infections. Enjoy a cup of tea, sit back and relax! Oh, and get as much sleep as possible. I know this is something we all strive for, but when you are infection-prone it is very important.
Cut out all refined sugars from your diet. This was tough for me, but made a huge difference. Drink cranberry juice (Knudsen's is great) that has no sugar added. No juice cocktails!) It's very bitter tasting - I liked to mix it with ice and water to dilute. Added to fizzy water and it extra special.
Urinate before *and* after sex. This shouldn't be a problem if you're drinking enough water. Also, wash with warm water and mild soap after sex. Women's urethra's are very short -- bacteria can travel in there very quickly.
If all else fails, do the low-dose antibiotic. I started out taking it every day, but then soon started only taking it after sex. All in all, I was probably on it for 6 months. Talk to your midwife about the effects on the fetus. It is probably not a problem, though. I took it to handle the infection I got after TTC and they assured me it wouldn't harm the baby.
Good luck to you!!!