Why do i blush so easily....? Like when I'm presenting something to the class... BOOM my face feels warm!?

You hate being the center of attention.

Because you are shy i guess.

I guess it happens when you feel nervous or embarrassed. My face does that too.

Because you are nervous(anxiety)
Anxiety triggers this behavior by releasing adrenaline, which is the primary hormone involved in the fight or flight response that is responsible for anxiety. When you feel anxiety, your body responds like it's seeing a predator, and that creates an autonomic arousal that creates a host of changes in your body, one of them being a redder face.

It seems that this reaction can occur even when a person does not feel much anxiety, but it's not clear why. Chances are their body is still experiencing stress or adrenaline behind the scenes.