You could have a urinary tract infection, an STD like chlamydia or gonorrhea if you've had a risk for those, a prostate issue, or a host of other issues.
You'll need to see a doctor to get a diagnosis, and don't wait to do that. Lots of those can get very serious if left untreated. Let us know what happens.
If it's jock itch, or ringworm, you'd see some kind of reddish line, but usually you see that on the side of your pubic area. It would be more difficult to see under the testicles. It certainly sounds like ringworm, and it's in the right place for it. It's a fungal infection. There are different treatments for it, whether you want to go pharmaceutical or other ways. But it would have no effect on urination, and for that reason reference the above advice. A doc will quickly be able to diagnose ringworm, but the other symptom is unconnected to that and so again, reference the above advice.