What means are you using to feed him?
If you don't know how much he weighs, how can you determine how to feed him. A general rule is 5-7% of body weight at each feeding.
The scale also tells you if he is gaining weight at a reasonable rate.
How often is he fed?
What sort of formula are you feeding him?
For a healthy squirrel breathing is a quiet, almost silent, unremarkable affair. Is there anything unusual or notable about the breathing?
Are there clicks? Is it raspy? Is it fast? Is it slow? Is the squirrel lethargic?
Please review proper feeding techniques for squirrels. Without the caretaker realizing it the squirrel can get aspiration pneumonia, which can be quickly fatal. So you don't want to go down that road. (Just erring on the side of caution here.)
Stool problems with squirrels.pdf
The above article should help you to understand what is going on with the poop.