Not to dishearten you but I know I have lost a lot of muscle, but at the same time remember our bodies are changing and you have to work within these confines, as it were...
I have taken to high proten poweders and milk immediately after work outs and that seems to be helping stop the loss so far and sure it will help build fast. One thing you can google for muscle growth (no not sterioids) is called H.I.T. = High Intensity Training. There is a LOT out there on this and some of the biggest body builders in the world do these work outs.
Not that you want to have that much muscle but its a good way to start building, and you dont have to be in the gym for hours each day. Real quick premis of HIT is this:
-Work outs under 45min
-1 set of 7-10 reps
-*MUST* fatigue muscle to failure (meaning even if a gun was to your head you could not possible do one more rep)
-Full body workout no more then 3 times a week of you over train and stall progress.
I have put 2 friends and 2 co-workers on this program and they have all seen a difference in a few weeks, big gains but not silly amounts.
But dont gloss over cardio either tho...
Oh and while you are google'ing, if you do, check out Author Jones (inventor of HIT), Ellington Darden (revised HIT), Casey Vader (HIT body builder), and Mike Mentzer (Amazing HIT body builder, RIP)
And not that I am trying to sell you, but just you know I am not a weirdo, I used to bench 285lbs, leg pressed 1144lbs, and ran 3 miles without much issue, weighed 220lbs and nothing jiggled
...
Enjoy,
Jason