Whenever i go boxing at the heavybag, my middle knuckle bone starts to hurt after a few rounds, what should i do i wanna get back to my boxing please!

Check for fracture: I would first get an x-ray to rule out a fracture, nonunion, or non union. Given your history of bone metastases and bone infection, these also need to be excluded as possible causes. Your oncologist or infectious disease physician are good resources to consult. Better taping and padding may also help.

See pcp: He might get an x-ray ; give you an answer- ice the hand down after work out.

See your PCP or an -: Ortho to get investigated with xrays, to assess what's happening. You seem to have had bone infection ; bone metastases, and that would be important to know more about, like where is the primary, etc. You might need a bone scan to be better evaluated. Don't do any boxing till you are investigated ; cleared to do so. Good luck.