9 months is a growth spurt time... and their intake needs increases.... and it reflects their growing and development needs.
Our Pediatrician... says to feed on-demand for the 1st year. For the 1st year, a baby's PRIMARY source of nutrition is from breastmilk/Formula... NOT solids and not other liquids. And they should still be fed on-demand 24/7 for brestmilk or Formula. And it should be given before solids... not after. If giving the bottle/breastmilk after solids... this is done to "wean" a baby.
I would not deny him feedings at night, if he is hungry. I'm sorry, but I disagree with your Pediatrician saying don't feed him.
Each baby is different... with different needs and appetites.
My kids when they were babies, had HUGE HUGE appetites and during growth spurts. They would wake too, and were simply hungry. Really hungry.
Also keep to regular naps and nap times. My son at that age was napping 3 times a day. 2 at the least.
If a baby is over-tired... they do not sleep well and wake more.
Sleep "patterns" in a baby always changes... and if reflects their changing development/cognitive development/motor skills, as well. It is not set in stone.
9 months old is a big developmental change, and he is simply changing. He is not a newborn anymore. And at 1 year old, they change a lot again... and their sleep.
Every 3 months is a "growth-spurt."
All the best,
Susan