Itchy red penis shaft, no sores...Jock itch or STD??

My penis shaft has become very itchy and red in places. There are no sores or anything...just extreme itch (if itched, redness & minor swelling occurs, but soon subsides). I don't know if this can be jock itch because it normally it manifests the inner leg and not the penis (or can it?). I have been with my girl friend for an extended period of time and have not had another sexual partener for 10+ months. Can anyone give me some insight? My girlfriend has been away for a while and if she sees it like this she will think something is up.
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