What should I do w my milk?

Hey guys so I’m a FTM I had my baby on Wednesday. So he’s currently on a formula supplement because of his weight loss, so his PED wants me to breastfeed first, then give his special formula after, and she recommended I pump after feedings to help kind of build up my supply. What should I do with the milk I’m pumping out? Because I love to breastfeed my son, but I also will be returning to work in about 14 weeks. Right now im currently making about 1oz from both breasts which is fine, since my baby is literally only 3 days old. I started off making barley 10 mL of milk on day 2, so I know my supply is increasing, but is like 1/2 oz enough to bag and freeze? My boyfriend said what I should do is open a bag and start slowly filling it till it’s full and then freeze it but I don’t know how sanitary that is. I’ve been bottling them and putting them in the fridge, but since I’m breast feeding and then doing formula it just kind of sits there, I only used 1 bottle I pumped when we went to his dr appointment, I fed him with that while we were out, because I’m still kind of shy about breast feeding in public. Thanks mommas! 🫶🏼❤️