I got swelling behind last teeth on my left bottom of my mouth for 5days.yesterday i noticed a big bump right behind swelling-it's painful to swallow.

Swelling gums: You may have an infection called pericorinitis. It usually happens behind wisdom teeth and infects the gums around it which spreads and gets into the lymph nodes. Go see a dentist right away, you may need a prescription of antibiotics.

See Dentist: This most often is an infection (abscess) and you need to be seen soon.

Floss tooth!: While seeing a dentist may be the obvious solution, after 5-6 days of probably knowing such (and not doing it) you might want to at least attempt to address the issue on your own by flossing the area of concern. Most often these are wisdom tooth "cleaning" issues. If the problem does not resolve or swelling interferes with your breathing then i agreed you should see a dentist.

Abscess?: It could be an infected impacted wisdom tooth that caused an abscess when it was not treated . Have it checked out and try to clean around the affected area through flossing and brushing.

Operculitis: It's possible you have an infection in the gum tissues behind your last tooth. This typically can occur if something has gotten caught under the gums which causes them to become inflamed. Schedule an appointment with your dentist to determine the exact cause. It could be as simple as just irrigating the sulcus behind the tooth to dislodge and flush out the foreign object.

Go to dentist: Pain on swallowing means it is infringing on your tongue space. If this is a dreading infection it could be very serious.

Swelling + lump: It may be a wisdom tooth finally trying to come in, or a cyst around an impacted wisdom tooth, or an abscessed 2nd molar, or one of dozens of other causes. As it is painful to swallow I would be inclined to think this is some sort of infection. See your Dentist immediately.