15 is a hard age for most people because you're really between childhood and adulthood, so you're starting to seek individuality, greater privacy, and thinking about stressful things like relationships, graduation, and what comes next. But, everything gets sorted out. You need someone to talk to, probably a therapist. A therapist can be sort of friend, but in your case can help you practice your social skills, problem solve, and feel better about the future.
OCD usually fades in time. Try not to stress out about it too much, unless it's really interfering with your normal functioning. As far as social skills go, give yourself permission to f- up in social situations, because a lot of social anxiety is addressed simply through practicing in social situations. You're behind others in your social skills, but the only way to catch up is to socialize, and not beat yourself up even if your brain is telling you that you did something wrong. Everyone screws up in learning social skills. Practice makes perfect! Now, the easiest way to connect with people is through volunteer work or joining a club of some kind because that way, you connect around a common interest rather than personality. Also, practice your social skills where maybe you feel a little bit of power and skill, such as talking to a waitperson, a neighbor, a family member, and so on. Broach new topics with people you feel comfortable with and see how it goes.
Given what you wrote, it sounds like you're depressed. In fact, what you wrote about yourself (no humor, worthless, bad skin) is just the mean stuff of depression. None of it is true. When the brain gets sick, some people get dizzy, others get forgetful, still others get headaches, and others get depression. You need to take care of yourself -- eat right, exercise, engage in hobbies by yourself (like drawing or hiking or puzzles) and should really see a therapist or talk a smart adult you trust, perhaps a teacher. You'll get through this sooner than you think. You'll be okay.