It's normal to have a small penis while you're sleeping- when you're not erect, your penis is very small, and that's normal. It shouldn't be large unless you are sexually aroused. Also, if you have very little sexual experience, it is normal to ejaculate without actually having sex. This should probably subside as you gain more sexual experience. Do you masturbate at all?

If you are weak and can't walk properly, you need to see a doctor. That is a sign of some illness that is not related to sex.