I have a toothache, I think it is infected, it hasn't been too bad but all of a sudden tonight my lip went numb, how serious is this, will it go away?

With treatment. Painfull tooth with numbness is usually caused by an abscess at the end of the root causing pressure on a nerve. This is common in lower molars and bicuspids when patients wait to long to get treated. Root canal or extraction will solve the problem. Also you should probably be on antibiotics. See your dentist asap!
Get it examined. Toothaches are often a sign of exposed inner tooth structure (the dentin which is what covers the nerve of the tooth). If decay or damage to the tooth is significant, infection sets up. The lip numbness may or may not be related to the tooth problem. The only way to know for sure is to have it evaluated by a dentist. Get it checked as soon as you can.