UTI Symptom?

Patient: My 11 month old son’s penis (urethra) is red and swollen. Being that it’s a weekend, I would like a word of wisdom before running off to urgent care. Is this likely caused by irritation (friction) in the diaper, soap in the bath, or could it potentially be a UTI that needs to be addressed asap? I realize it could be any of those. Also we are currently switching him from Similac to whole milk, not sure if that plays into it. Thank you for any advice you may have.