Hi there, The size and girth of your penis has little to do with satisfying your partner. You need to learn the art of foreplay. You're anxiety about all these things is most likely causing the premature ejaculation, and weak erections. Masturbation is a healthy activity as long as you're restricting to when you're sexually excited. Read about and start doing Kegel exercises for the pelvic floor muscles. For the rashes, I recommend you to see a skin specialist. Good luck.