If you are in an aggressive calorie deficit -which you are-even if you are not working out, you still need to be getting in a MINIMUM protein amount of 1g per lb. This helps prevent against muscle break down in addition to lifting weights. If you do these things, you will still probably lose muscle at the calorie deficit that you are presently at. These are basic fundamentals of diet, nutrition and fitness. Instead you are eating at a ridiculous calorie deficit, not lifting and not hitting minimum protein requirements. This is exactly why you are 5'10, 145lbs at 13-15% BF. You are not ready for steroids...not even close man.