I'm working on getting back in shape for lacrosse season, which means lots of running. I've been running 3 miles a day for the last few days, and intended to continue running 3 miles a day for the next 3 weeks or so, but today a friend mentioned that it is unhealthy and counterproductive to run that much. Is this true? Am I doing too much running? Is there a limit to how much running I should do per week?