Skin Problems? Please help!

Hi there! I have a few questions regarding my snake's behavior and skin. He's a 10 months old corn snake, and as this is the first reptile I've taken care of, I'm not entirely sure if what he's experiencing is normal or not.
About two weeks ago I've noticed that some of his scales are losing their "glossiness" and some other scales look slightly wavy or corrugated. Since it was only about 5-7 of them that looked like that I thought that maybe he manages to get scratches on his skin from his environment in the vivarium but this continued to appear on his skin days after. Today I've noticed that he's got some yellow spots under his head and a brown stripe close to them. This is not dirt as I've tried to wash them away but those wouldn't come off.
Also, since I've changed his substrate/ground with something called "JBL TerraBasis" he keeps burrowing and hiding under it, then he goes through this water bowl, then back into the ground and water and so on. What I mean by saying this is that he's started going through his water bowl very often, much more than he used to. He's also submerging his head under the water and makes a sneeze similar sound when he comes back to the surface. Do you believe he's too warm? Or does it have anything to do with the humidity?
Another thing would be that at night (when he's most active) he desperately tries to escape his vivarium and when I get him out, the first thing he does is to poo everywhere. Is this normal or is there some underlying problem I'm overseeing?
Do you know what could cause this behavior and the symptoms I've mentioned above? Any help is appreciated, thank you beforehand!!

First of all, anytime a problem is detected a visit to the Vet would be more prudent than asking folks on an internet message forum.

Also, it would help if you posted pictures of the problem. It's hard to understand what you are describing.

Snake's skin takes on a dull lack luster look prior to shedding. It could be he's about to shed. They also will soak in water sometimes as a way to soften their skin.

They will sometimes soak if their skin is irritated, as with some type of parasite, or burn. Perhaps he has mites, or perhaps your heat is too hot and he has been burned.

Some woods (mostly in the pine family) which also includes cedar, spruce, and any variety of Pine, contain resins in their sap that irritate snakes, and can even be fatal. No Pine Wood of any type should ever be placed in a corn snake's cage whether it be bedding or sticks to climb on.

Since I don't know about the bedding you are using, and you have provided no pictures of your cage or the snake, it will be almost impossible to render any help.

My suggestion, go to a Vet immediately.