Husband has scrotal infection

[justasking_]

My husband has been having scrotal pain and a small lump.  He had an ultrasound and found no cancer.  He says the Dr. said he had an infection and perscribed antibiotics.  He says the Dr. didn't run any other tests.  I am assuming this is epididymitis.  He is uncirumcised and doesn't have any other symptoms of an infection (UTI).  What would be the cause of this?  Is it from an STD otherwise?  Shouldn't the Dr. have done at least a urine test to check for an infection?  He claims it can't be an STD because he hasn't cheated but of course he would say that.  Do I have reason for concern or could he just have an infection for no apparant reason?  He says he had a mild scrotal injury from a ball when he was young.  He says he hasn't had a sex drive for a couple of months and the Dr. says that this was the cause and was normal but how could the Dr. know it was an infection and what type to treat if she didn't run any tests?