I have been having mild to not so mild pains in my chest, and now I feel like I am bruised on the inside. What might it be?

There is absolutely no way to give a diagnosis online. If you're concerned about this then you'll need to see a doctor.

When a person has chest pains, they should always go to the hospital immediately. It could very well be nothing. On the other hand, it can be a heart attack. Since one of the possibilities can be fatal, you don't wait around.