My orphaned baby bunny eats alot but wont pee even when I wipe his butt with a warm wet cotton ball. ?

I feed him puppy formula ( basically goats milk) and he eats about 2 to 3 eyedropper of it and i stop because his stomach looks like a balloon. am i over feeding him? and he wont pee. he only peed like yesterday morning! im worried and i know the mom wont do anything for it bacause she let the other ones die and i got this 1 just in time. any info would be soo helpful!