What dosage of amoxicillin for my 23 pound 9 month old?

Varies. The dose of Amoxil (amoxicillin) depends on the infection being treated. For most things it is ~45mg/kg divided twice a day. So your child would receive probably the 250mg/tsp formulation with instructions to give it twice a day (note: amount given doesn't have to be precisely what is calculated, so long as it is close). For ear infections the dose is higher, usually 80-90mg/kg divided twice a day.
For what illness. For ear and sinus 400 mg twice a day for ten days.For other more concerning infections it may be different.
What your doc rxs. This public site was not set up to bypass your regular doc.We don't provide diagnosis or treatment. Antibiotics can help when indicated or mask certain serious problems when given inappropriately.I recall one parent wanting this sent out with no assessment,kid was found to have bacterial meningitis, in hospital 10 days. These drugs are dosed by weight and condition treated. Sort that out first.