I've only ever had sex with one girl and it was her first time. Today, however, on my way to hockey practice, I noticed that on the side of the head of my penis I had a red bump. I didn't think anything of it. After practice I noticed that the skin that had touched the red bump during practice had looked discolored. Almost as if it had scarred. Is this a bacterial infection or something else?
"Whoever commits adultery with a woman lacks understanding; he who does so destroys his own soul. Wounds and dishonor he will get, and his reproach will not be wiped away" (Proverbs 6:32-33).
You didn't state how long it has been between the time you had committed fornication (having sex outside of marriage) and when the bump showed up. It is a piece of information that the doctor will need to know. You need to immediately see a doctor and have a complete set of tests for sexually transmitted diseases. You have an infection of some sort and it needs to be treated immediately. Delaying can only make matters worse.
While I can take your word that it was your first time, I can't take your word or her word that it was her first time. Nine times out of ten when I talk to boys in your situation they were given a line that it was the girl's first time. When they quietly asked around they were shocked to learn that several other guys claimed to have had their penis in the same girl. Even if she hadn't had sexual intercourse, she could have done oral sex which transmits sexual diseases just about as readily as intercourse.
There are numerous reasons why God said that sex is to be limited to only those who are married. You found one first hand. I hope it is something treatable. But please realize that the reason God gave these laws is to protect us from harm -- physical, spiritual, and emotional harm. "And now, Israel, what does the LORD your God require of you, but to fear the LORD your God, to walk in all His ways and to love Him, to serve the LORD your God with all your heart and with all your soul, and to keep the commandments of the LORD and His statutes which I command you today for your good?" (Deuteronomy 10:12-13).