Sorry I am just seeing your message. Ironically I am battling another UTI myself right now! However I can tell you that I do know how to prevent them and I just got lazy this time and didn't follow my own rules! Here is what to do:
1. Always drink a lot of water on any day you might be having sex with your partner. This is the number one most important thing. You just want to keep liquid moving OUT of your body at all times. Drink water before and after sex, and all day long the day of sex and the next day.
2. Peeing after sex is important, but wait till you have enough pee to make a good flow. A few drops will not cleanse the urinary tract enough. You want to really be peeing a lot, even if it is an hour after sex. (This is counter-intuitive, but it is true.)
3. Take preventative supplements in fairly large amounts on the day you have sex and the next day. I like d-mannosse, but you could also use cranberry tablets. The really important thing here is the large amount of water, but the supplements help too. I usually take 4 d-mannosse capsules 3 times on the day of sex and 3 times the next day (along with all the water).
4. Be very careful about alcohol and Sugar on the day of sex. Alcohol dehydrates you making you pee less (but you can counteract this with huge amounts of water) and Sugar lowers your immune system making you more vulnerable to UTIs.
When I follow these rules I am able to prevent UTIs 100% of the time. The water is really the main thing. You just can't let those bacteria sit in your urethra/bladder, period. As long as they get flushed out asap, you will not have this problem!
There is also a wonderful book you might want to get called "You Don't Have To Live With Cystitis" by Larrian Gillespie MD that really helped me with all this.