Been having pain in neck area under the back of my left jaw and in neck at base of skull, also dark red spots under tongue. related to infected tooth?

Pain: You have an infected tooth that needs to be treated. I can't tell you if the pain by your jaw is from your tooth or something else, but your dentist will be able to tell you. See your dentist ASAP.

Please see a Dentist as soon as possible. If you have an infection in your tooth it can spread and be dangerous to your health and well-being.