A.,
I hate to say it, but I really dont think there is such a thing of eating too much at this age. I too have a 5 month old, and she eats 6 ozs almost every 3-4 hours. About 42 ozs per day. This is starting at about 5-7 am and going until 10 pm, She sleeps through the nite.
On top of that, she is given cereal in her formula to thicken it up, (about 1-2 of the formula scoopers of rice cereal.) Plus once a day she gets one of those plastic containers of gerber 1st foods, usually fruits, shes not to big on veggies yet.
I would say, if you are uncomfortable with the way your ped handleded the situation, I would move on... Mine has never yelled at me, or made me feel like I was doing something wrong.. afterall, you are learning for the first time, and unless you call him everyday with a new questions, you need to learn by trial and error.
I have bounced back and forth in my doctors office with both my kids, and neither doctor minds, (its simply an getting an appoitment conflict for us, but they wouldnt probally know any better)
Good luck!