I don't get it. Building muscle will help you burn fat and keep your metabolism high. Working out is very easy if you do it right (most people don't, even those who "know what they're doing"). If you are losing weight, you're losing muscle. You have to at least keep up with this.
1) Drink lots of water.
2) Space out your meals and eat lots of protein.
3) As before cardio to burn calories, increase metabolism during the day, for heart health.
4) Weight training is good. If you do more than 15 reps, you're not building muscle. You're burning calories, but that's it. If you don't stress yourself to the max every time you work out, you won't build muscle. I recommend doing 3-5 reps of each exercise, max you can do. Work out one muscle group. Then lots of rest for that muscle group. Next time you work out, do the same but with a different muscle group. If you aren't sore the next day, you didn't use enough intensity. If you can't lift more weight the next time you work out, then you didn't give yourself enough rest. Make sure every exercies you do you are going for intensity not duration, except for cardio. Cardio will help you lose weight and burn calories, but it won't build any muscle.