Hello. I'm sorry you're having problems. While a severe reaction to poison ivy could conceivably alter your immune response and make you more susceptible to an infection, it isn't necessary to attribute your UTI to the poison ivy dermatitis
. Women frequently get UTIs following intercourse -- doctors call this "honeymoon cystitis" -- whether or not they have concurrent medical problems. Honeymoon cystitis is more likely to occur when women don't empty their bladders immediately after sex, if they have a new sexual partner or if their vaginal area is already irritated for some reason. (You didn't mention if your genital area was involved by the poison ivy, but this could be a contributor.)
In any event, you should see a physician about your urinary symptoms. A short course of antibiotics should address this situation if it's a "run-of-the-mill" UTI. If not treated promptly, a UTI can get progressively worse and lead to serious complications.
I hope that helps, and I hope you and your boyfriend feel better soon!