I had stitches in my knee & it's been 2 weeks & i can't tell if it opened back up or not. it's bleeding but i think it's just from the scab?

Get it checked.: It can be a wound hematoma (blood collection). Hematoma or wound dehiscence ( incision separation )can become a nidus for infection and need to be drained and washed out at times .Your doctor will make that decision , but he need to have a look at it . So show it to him as soon as possible ,since Joint or knee infections have to be treated seriously.