Ditto what the others have said - if you feel generally ok, then go ahead. Sometimes with UTIs I feel run down and a little nauseated, and other times I feel ok (except for the UTI pain itself.)

Last time I had a UTI I did a 200 mile ride right after starting the antibiotics. I took extra precautions because the antibiotic I was on said it would make me sun sensitive (and this was September in the Bay Area - hot and sunny.) I was practically white from sunscreen but made it through no problem - and no burns.

The antibiotic also said it might affect balance but I didn't really notice being any more unbalanced than usual.