My gum and teeth hurts really bad whenever I bite down. What is happening?

Best to see dentist. It could be a number of things including a tooth problem or a jaw problem.
Must see dentist. Something is causing inflammation and / or pain in teeth or gum. There is definitely something wrong: could be gingivitis, gum disease, infection in the gums, a vitamin deficiency, dental cavities, root canal problem, abnormality in your bite, part of a systemic disease affecting the nerves or vessels leading to oral cavity (pretty good for a non-dentist, eh-:). So, go see a good dentist.