Thank you very much,I have been to my gynacoelogist too.
Simply tell him you have one, its not like its an STI, they happen. You'll get a medication, and get over it, I'm not sure if it is contagious or not, but looking up quickly about UTI's in women, sex is most common cause for a UTI which is caused by the frequency in the amount of sex you're having. (apparently extremely common in newlywed women), women are more prone to them than men are. etc
I'd say that to be safe, dont have sex til you've completed the round of medication and are sure the infection is gone. And if you are on birth control, use condoms as back up( Some antibiotics make birth control less effective)