patchy brown color on penis and scrotum

[bchang]

Hey, I'm a 20 year old asian male, average weight. Last week my girlfriend came out to visit and we engaged in a lot of sexual behavior. After she left I noticed that there are now a few brown patches on my penis. I am uncircumcised btw. One is about an inch long, a quarter of an inch wide on the top of the shaft, there's a little larger one on the underside which is also a little bit tinted red which is also very smooth to the touch. There are also some discoloration towards the top of the penis (without rolling the foreskin back), as well as some smaller brown marks that are kind of like curved lines about a half an inch long on the shaft as well. There is none of the brown discoloration beneath the foreskin or on the glans. I'm not sure if it appeared all at once or if it was somewhat gradual but I know it was not there the week before she got here. I'm not concerned about std's since she was a virgin before me and we've been together for around 5 months with no problems. What concerns me also is after noticing that I noticed that there are some small brown patches on my testicles as well, not widespread, coming up from the darker area at the back of the testicles up along the sides of them. It's been 7 days since I've noticed the patches on my penis, I'm not sure if they're getting lighter or not so I don't know if it could be bruising, but it seems unlikely I'd bruise my testicles in such a way. This has been causing me a lot of anxiety as cruising the internet (which is dumb and just a panic attack waiting to happen, I realize) as I have heard all sorts of things about fungal infections or cancer or whatnot. What could this be?