In English, American English at least, we don't really say 'to do sport' like how it's used in Russian...like when referring to 'exercise' type activities, like: running, yoga, weight lifting, gym stuff, etc. In your example, we would just say '...he recommends I exercise 3 days a week.' Usage of sport is usually restricted to playing some kind of game/sport like soccer, basketball, tennis, etc. Swimming might be referred to as a sport if it's on a team or as part of some kind of competition or club...otherwise I'd just refer to swimming as exercise. We could say: "what sport do you like?" "did you do any sports in school," "I like playing sports," etc.