If i haven't kissed a girl by 19,should i just throw in the towel?

You shouldn't give up, but you also shouldn't continue doing the same things -- or you'll get the same result. You need an attitude change. Get out, work out, improving your physique. Don't quit hobbies that you enjoy, but don't let them hurt your lifestyle (by not exercising, etc.) Go out and get some phone numbers and start dating.