couple weeks ago i stopped lifting weights and started doing cardio - I run 3-5 miles 4 to 5 times a week. been doing this for about 3 weeks and i lost weight and feel great. but the downside is i definitely shed some muscle mass. so i'm thinking about lifting weights again, but i don't wanna give up the cardio. so i plan on doing both - maybe switch off doing one and the other. is this a good plan? is this just gonna slow my muscle gaining time? what do you guys think?