I have lost a lot of weight, but I have also lost some muscle mass due partly because I left the gym for 2 weeks because I had the flu. But I'm back into practise. I started HIIT which is High Intensity Interval Training. Basically you run on a treadmill, you have a constant speed number which we'll say is 3.5 and you walk that for about a minute then you start to sprint at a speed like 7.5 for 30 seconds. Then go back to 3.5 for a minute, then sprint again except you change the sprint speed to something higher. Anyway, the more you "damage" your muscles the longer it takes to repair therefore more calories and fat are burned in the process of repairing those muscles. You'll still be burning calories hours after you've left the gym. And it speeds up your metabolism like nuts.
I've included fish in my diet, but I still don't eat other meats like chicken or pork. My sister talked to her trainer and apparently your body needs meat like turkey, chicken, and some red, in order to gain muscle and lose weight due to the high protein intake from those meats. But fish is still good, so Im not complaining. It's just that it will take longer to gain muscle because I'm on a vegetarian/pescatarian diet.