You're not training any longer, so you're not seeing gains.
Structure your runs so that you're alternating a tough run with an easy one. If you are normally running, say, 2 miles a day, you should change your schedule so that you run 3-4 on one day, and only 1.5 or less on your 'rest days'. This allows you to rest and recharge, without getting nothing done. 3 tough runs a week, 3 easy runs a week, one full day's rest. Every other week, make your last 'tough run' for the week an all-out run 'til you drop exertion. I'm talking marathon 6+ miles here. Then either take your full day off if it's scheduled, or take two days off if you REALLY exerted yourself.
But, your running schedule will serve to get rid of excess fat more than build muscle. If you're already a member of a gym, start your workout routine. Ask for advice from the trainers there: they're there to offer it.
Basic formula to a workout routine is as follows: use comfortable weight levels so that you can do 8-10 repetitions (ie: a single lift and lowering) multiple times. 3 sets is a good start. Set 1 should feel relatively easy. Set 2 should be somewhat more difficult. And set 3 should be tough to complete. When in doubt if a weight amount is the right amount, go smaller. You should err in favor of MORE sets (not more repetitions between resting... it isn't necessary) rather than LESS sets.
Again with weightlifting, always give a worked muscle group one day's recovery time. You can effectively lift with the same muscle group 3 times a week (unless you're experienced and in great shape). I would recommend working out every other day, with one two-day rest a week. Make yourself two 'weight settings' for your workouts. The standard should be used twice in your week, the more difficult should be used once per week, and you should take two days to recover every time you go all-out and use the heavier weights/more difficult workout.
The final part to your routine is diet. If you're running enough, you need not worry about consuming carbohydrates because odds are good that you'll be burning them off. Otherwise: you should just cut down on 'em. Make sure you're eating at least two of the following every single day: carrots, broccoli, spinach, green peppers, green beans, asparagus, romaine lettuce. Restructure your meals. Make them smaller and ALWAYS consider a meal in terms of nutrients gained from it. You should always have at least SOME protein-containing food in every meal. Try to tend toward the leanest source of protein possible. In order: whey protein shake, unsalted nuts/protein bars, fish (tuna out of the can works), chicken/turkey, ham/pork, beef/steak. To compliment your protein, you should be consuming either a fruit or a vegetable. For the third component of the meal you should have a small amount of some sort of fat (dairy, vegetable oil, the included fat from beef or ham) OR the aforementioned 'almost unnecessary' carbs (tend toward non-empty calories; ie: instead of white bread have wheat/rye/whole grain, instead of white rice have basmani, instead of pasta have wheat pasta).
You should be eating 4-5 times a day instead of the normal 2-3.
Most important of all: water. If you don't fill and consume at least one Nalgene bottle worth of water in a day, you're not drinking enough. That's not to say you're not getting enough, most people tend to make up for lacking water intake with extra food intake. Most of the time you're hungry, you should drink water first, then see if you're still hungry.
I hope that helps.
