You lost 5 pounds, mostly because you emptied your bowels (all of us have stuff moving through the intestines, it takes 1-4 days to empty the bowels) and most likely because you were not getting sufficient fluids.
I seriously doubt you lost 5 pounds of muscle, maybe a couple pounds of fat - IF you are fat.
So mostly water was lost.
Supplements in general should be something like a one a day type multivitamin (everyone most likely should have that).
If you are heavily weight training to build muscle, supplement with protein shakes. They help to gain weight and provide your body with the protein needed to build muscle.
If you are doing maintenance workouts (not building muscle mass) you should be able to get all the protein you need from a normal diet.
Mind these are SUPPLEMENTS not Replacements.
The first and foremost important part of a training program is the diet. If you eat a lot of refined sugar, added fats and rely more on starches and grain products instead of eating good vegetables, you have screwed the pooch.
Veg and fruit are good for you and provide the basic nutrients you need in a form that is more readily used by a healthy diet.