Buliding Muscle And Cardio For Hardgainer?

I'm going into the army and trying to get bigger but also do cardio twice a week but weightlifting 3 times a week. I used to be 7 stone and now weigh just under 9 I am 5Ft4, when I run I do around 2.5 - 3.5 miles depedning on the route I take to prevent muscle loss what should I do before or after a run to maintain mass but also good cardio. Answers from people who know what they're talking about will be appreciated.