During which month do people sleep the least?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

A man calls his dog from the opposite side of a river. The dog crosses the river without a bridge or a boat and manages to not get wet. How is this possible?

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?

I’m tall when I’m young, and I’m short when I’m old. What am I?

I don't get anymore wetter, no matter how much rain falls on me.

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?