Left ankle swells after i work out. foot tingles and shooting pain down leg from back. i have flat feet too. xray & ultrasound normal. what is this?

Arch support: Not enough history given . If the pain starts in your buttock and goes all of the way down the leg to your foot then it is likely a radiculopathy--problem with a lumbar disc. If pain just in lower leg and foot could be just a foot problem but possibly still involve lumbar disc. Get good arch supports/better shoes to see if that helps. If not, see your doctor--possibly have lumbar spine MRI done