Breastfeeding question

Alexandra • i’m so blessed to have two beautiful babies after infertility ❤️🙏🏻TTC Baby #1 since Aug 2017 .. Positive pregnancy test 12/23/18 🙏🏻 Baby Boy due September 5th💙👶🏻💙 Nicholas Salvatore 9/2/19💙💙 TTC BABY #2 since November 2019.. Positive pregnancy test 11/4

So my son is about to be 11 months on Sunday I’ve been ttc for about 6 months now. I actually needed to have surgery last week with my fertility specialist and he recommended i stopped breastfeeding because i need to get pregnant within 5-6 months otherwise I’ll need this surgery again .. i get my period next week and he wants me to stop by my next period to put me on fertility meds. i don’t have enough stored breast milk to last a month probably more like a week. Now my question is what should i do because i can’t get in touch with my pediatrician super crazy office I’ve been trying for the past week should i just give him my milk mixed with regular milk bc i May have enough if i mixed it to last me atleast 2-3 weeks or do i have to give him formula I’m so confused