I've had four wisdom teeth extracted 7 weeks ago and it seemed fine until yesterday my left cheeck swollen a bit.can you tell me why this happened.

Nope: Not without seeing you. No way to know if it is related to one of the extracted teeth, another tooth, of dental origin or even non-dental and medically related. I suggest that you start with seeing your dentist.

Swollen cheek: In this area in the cheek by the excised wisdom teeth, is a large lymph gland called the parotid gland. It can become infected and swell. Ice it tonight but call the oral surgeon and ask for another x-ray and exam. Sometimes wisdom teeth can have more than 3roots or they could have been crooked and not come out cleanly.