Why is the back of my tounge really painful? it makes speaking, eating and drinking really discomforting it has been like this for four days now

See a doctor: You may be infected. The condition may be serious so seeing an throat specialist is important.

Probably minor but..: A sore tongue can occur from 1. Repeated biting on it (biting it makes it swollen, swelling makes it more susceptible to biting it) 2. A virus like lesion (think "cold sore" 3. A sharp irritant (a "chipped" tooth) 4. Something less probable, but potentially far more serious. It would be wise to see your dentist if there is no obvious cause and /or it doesn't heal in a few days.

Can't be sure. : What have you done to it? Taken? Had to drink? Had to eat? Need lots more information to guess at your particular concern. See your dentist for an evaluation.

See a doctor!: It's time to see a physician or dentist to find out why. If that is your only symptom, start with a dentist. If you have other symptoms or it feels like perhaps it's more your throat, see a physician.