Q: I was sick with strep throat for 2 weeks and couldnt work out how much muscle have i lost

A: If you haven't lost any weight, then you didn't lose any significant amount of muscle. You probably lost some strength in any case, but that will come back as you restart workouts. If you did lose weight then you probably did lose some muscle, but as with strength rebuilding just-lost muscle is much easier than obtaining it for the first time. As you start eating normal again and get your weight back up, the muscle will come back.