Some penis questions, like: very little white dots on the foreskin, black corona or whatever it is etc...

I'm 15.

I've got tiny very little white dots (maybe rash) on the bottom of my foreskin, you can see it better when I pull my foreskin back a bit  when erected (can't pull back completely when erected) it doesn't itch or hurt, it doesn't have any symptoms just those dots/rash. Do you know what it is or do you think you know? What is it?
For sure it isn't that thing that is at the end of the glans (glands) (corona) and has got funny name, it's not that.

My corona (don't know if it is a right name, it's the bit where the glands end) is black, I'm really scared, it looks like it's dead black but it's still sensitive, do you know what it is?

Also I can't pull back my foreskin when erected, it goes only about 20% back when erected and then it's uncomfortable to pull more. Do you know why and how can I stretch it or something?

Also my glands are sensitive, it hurts me when I rub it but it doesn't when I touch and push it. Why?

And sometimes my balls, and skin around the balls is VERY itchy, it may be itchy for an hour and then it feels again normal, but it's itchy everyday. (maybe because I'm allergic or because I wear bad panties xD). Why?

Also I've got some spots (with colour of skin) on the sides and bottom of my penis, and on the balls. (It isn't itchy or doesn't have any other symptoms but it may be related to above question (It also may be something allergic, I'm not sure) Do you know  what it is?

I need to have answer fast because I may have sex in this month or next. Please answer. :)
Thanks.