How to build muscle while losing fat not muscle mass.?

Im about 200 pounds, 5'7. I just started working out no more than 6months ago. I have a good weight lifting routine(day 1-chest and back, day 2-biceps and triceps, day3-shoulders and legs) and i try to do cardio everyday and core a couple times a week. I go to the gym 4-5 times a week and take 2-3 days off and change my routine often to avoid muscle memory. I seem to have hit a plateau a month ago, i lost 30 pounds but havent gone under 200 yet. Any tips?