l brush very good and rinse well.The problem is, 10 minutes later my mouth starts to feel like something is in it.l then run my finger on the inside of my cheek and there is a transparent-white substance all over my finger.This also happens when l wake up in the morning. Anyone have a clue?
also does it mean something is wrong with me? or is it normal? is it bad for the tissue to be coming off like that?

If you are using an alcohol mouth rinse, it could be burning the tissue. The white stuff is sloughed off tissue.

In the morning, meh. That is just typical morning mouth. Saliva flow really drops during the night. Some people breath through their mouth which dries out the tissue.

What kind of toothpaste are you using? Many people have a reaction, like you're explaining, to whitening toothpastes. Try switching toothpastes and see if it goes away.