About 3 weeks ago the head of my penis started feeling very tender and had sort of a reddish color to it after sex, masturbating, and sometimes showering. I also noticed that around the edge/head of my penis also looks sort of swollen and has a purple tint to it after sex and masturbation in some places. It usually goes away the next day until I have sex again.. I have been in a stable relationship with my girlfriend for over a year so I dont think it is an STD. I have read that sometimes a change in shower gel or soap can cause that...last time I bought body wash I got the "Cheap" brand. Should I be freaking out?