What Does A Big Bump On And Red Patch On Penis Indicate?

Here are all the problems that i have. I have 1 big bump on my back which when pressed pushes out white dry stuff which smells more or less. I also have 1 red patch on the head of my penis. It is so difficult to differentiate it from the surrounding skin.

I went to see a doctor 4months ago, he said it was nothing. I am scared that it might be some STD or something. I was with a girl for 2 and half years having sex without a condom. She tested herself negative for all STDS. Im still worried it might be something bad.