diabetes puts him at higher risk for some urinary issues even when he has good glucose control. he certainly needs to be seen and get some basic urine testing done as well as he needs a manual exam of his prostate done too.
unless you suspect him of having other partners, no reason to think std.
grace
Hi and welcome, it really would be best to have a doctor check him out. I not heard of an std that only flares up during those times. Could be coming from some other area and he thinks its from his penis.