I got a knee to the thigh which caused bruising. a couple of days later i felt some discomfort on the side of my knee. is this cause of the bruising.

Probably not.: Sounds like the pain is in a different area - thigh versus knee - makes me think of a meniscal injury or tear If this persists you might need an MRI of that knee.

Bruising:knee pain: The knee to your thigh caused a contusion (bruise) but although this is the first damage one sees, other damage can be done to your knee ligaments, which heal very slowly and would be noticed a "couple days later". Blood from the bruise in your thigh can migrate down to your knee (gravity), and the swelling can also cause mild pain.