Where I up I am constantly getting up and down to get stuff from the printer. Now my knees hurt, and I get a back knee pain near the behind area??

Probably overuse. Since this involves both knees, it is probably from overuse, especially since only the back of the knee. Take more frequent breaks to get up and walk around. Perform simple range of motion activities by moving the knee through full range of motion and stretch at the limits of motion when fully straight and fully bent. Ice may help if pain persists. Apply ice to painful area 15-20 min/hour.