This happened with my daughter when she was about the same age. She had to have a catheter twice. Once to confirm she had a UTI and once to re-check after taking antibiotics to make sure it was gone. I'm not sure why one of the other Moms would say that having a catheter put up your uretha is not painful, because it is...whether for an adult or a child. However, you do need to know if he does have a UTI, so it may be the only way to get a clean/pure sample of urine. If he has a fever and seems to be in pain when urinating and holding his private area a bunch, then he probably does have a UTI.
It is difficult to watch them put a catheter in your child. We just did a lot of praying and when it came time for the catheter, I was singing with my daughter. She did cry as she sang, bless her heart! Even more heart-wrenching was that IF it is a UTI, today's Pediatricians are taught to address the UTI aggressively. Not only with antibiotics to get rid of the infection, but also with addt'l testing at the hospital to rule out a more serious internal problem. We felt extreme PRESSURE to have the DYE-TEST done on our daughter at the hospital. That is where they put dye in your child's urinary tract with a catheter and then slowly take x-rays as they urinate it back out. It is painful and scary for a child and when they are under 2 years old they will not give them a sedative, etc. We felt so much pressure to do this, even though our daughter ONLY had this ONE UTI, that we changed Pediatricians. We ended up going to the hospital for a non-invasive procedure, a sonogram, to check for any obstructions, but decided against the invasive procedure after much prayer, discussion and counsel.
Lastly, given infections I had as a child as a result of "bubble baths" as well as this one UTI with my daughter, we have never let her take baths with soap in the water. I would wash her down with soap and water as she sat in the tub (no standing water in tub), but with running water...not sitting water. Then, I'd rinse the tub out and let her sit in standing "clean" water to play at the end of bath time with her bath toys. Now that she is 4 years old she only takes abbreviated showers. A year ago, we had added the removable shower sprayer that we use in the bathtub. So, she in effect has taken showers for the past year. Sometimes she still wants to play in the tub, so again, I do her hair and bathe her with the detachable shower head first (as she stands or sits), then, I fill up the tub with ONLY clean water for playtime.
Our daughter has NEVER had another UTI since that one time. We hope she never will again. We learned a lot about UTIs, we also learned a lot about taking in all the advice and counsel possible before making serious decisions about our daughter's medical care and help. We are thankful that we didn't put her through the invasive testing at the hospital, though we would have, IF she had had 1 or 2 more UTIs within the next year or so. It would have remained difficult, but we would then have felt it warranted to prevent further damage. And, she would have been old enough to have a sedative then too.
I provide ALL this lengthy info to hopefully help you in making a decision that you will feel comfortable with for your son. I know it is difficult. I pray that you will have the right input/counsel and instinct to feel at peace as you move forward in his care. Many Blessings - L.