How can i heal a cut on the inside of my lip?

The problem with trying to heal it is that you said yourself "im constantly biting the inside of my lower lip" which means that any healing at all would be disrupted by this. Perhaps a mouth guard like those worn by football players but based on what you wrote, the key seems to be getting to a dentist and resolving the cause, namely that you have bad teeth. No ointment, natural remedy or pill can work if you keep traumatizing the tissues.