Tell your pediatrician to go to hell. Excuse my bluntness, but you need to switch pediatricians. Children under 12 months old shouldn't be weaned. Babies that young can't overeat if you're not forcefeeding the baby. If you're giving him sufficient affection and cuddling, he's eating because he's hungry.
You can go to the Centers for Disease Control website and look for "Clinical Growth Charts" and plot where your child falls. They also have a section for children's BMIs, so you can get a reality check on your child's weight. A lot of parents with overweight children don't think their children are overweight. On the other hand, a pediatrician who thinks a nine-month-old should be drinking out of a cup needs her head examined.
When you switch pediatricians, don't go to a different one within the same practice, switch practices entirely. Don't tell them you're going or why. Ask for your child's medical records "for your own files." Then ask your neighbors who they like.
If the other pediatrician says the same things about your baby's weight, you may have something you need to get to the bottom of. I mean, if your baby really is that hungry and is overeating that much. Personally, I'd feel comfortable discounting what your current pediatrician says because he's stupid enough to think that babies under a year old should be weaned. But if the second pediatrician also has concerns about your child's weight -- well, I'd listen, then.
It also occurs to me that if you are feeding your child something other than formula in the bottle, that will cause your child problems. A lot of parents fill a bottle with sugar water, or juice, or soda, which is terrible. Juice is nothing but sugar water, really, and there are more vitamins in the formula.
Hang in there.