nipple sizes?

shyan
I really don't get these. My newborn only takes the dr Browns size 1, and slow flow nipples. He's almost 5months. When do I switch flows? I tried size 2 and he choked. The only time he gets size 2 or medium is when I put cereal in his bottle. (Fuck your opinion on that, I'm asking about nipples) I don't get these sizes lol. FTM.