What kind of ankle problem if there is pain esp after activity but no visible signs of swelling? swelling showed on xaray tho.

1) you don't need : To have swelling to have pain, pain can come without swelling. 2) usually, if there is swelling on an xray it would be seen clinically as xrays predominantly show bone. When swelling is seen on the film, I think it would be rare or a doc not to detect it clinically. Pain may be due to soft tissue injury I.e sprained ankle, posterior tibial tendon injury, sinus tarsi syndrome, etc etc get evaluated