My penis and testicles, except for a streak in between my testicle, have turned reddish and have started been itchy over the course of the last few weeks, some days it looks better some days it looks worse. i had sex about 3 weeks before it appeared?

This sounds like a non-STD dermatitis, probably unrelated to your recent sexual contact. There are many possibilities, mostly not harmful and easily treated. Try an over-the-counter treatment for tinea cruris (jock itch) (look for products on the same shelf as athletes foot treatments, or ask the pharmacist). See a doctor, ideally a dermatologist, if that doesn't clear it up. Good luck.

have MD check out skin gor any infection. In the meantime wash with soap and water-dry and apply OTC cortisone cream.

Please see a Urologist for a thorough examination to receive treatment recommendations.