Hi Bre Ann - you have a healthy boy there! If you still have your son in an infant carrier, he's already outgrown it as they usually only support babies up to 20 pounds so it is time to buy a new seat. My youngest only lasted 9 months in his infant carrier.
I would recommend switching to a convertible car seat that will accommodate him up to 65 pounds if it will fit in your car. The majority of them only fit up to 40 pounds. You probably already know that he will need to be rear-facing until at least 12 months - some recommend longer.
You could start him on a sippy anytime. He will be messy with it at first but will get the hang of it quickly.