Suggestions? Help?

I am supplement with formula because baby girl didn’t gain any weight from her first doctors appointment at 4 days to her second at 11 days. Up until that point I had been exclusively breast feeding. I was pretty upset because I felt like breast feeding was going well. I feed her every two hours during the day and then every three through the night if she allows. She usually eats for 25-35 minutes each feeding, sometimes a little less, sometimes more. Now with supplementing formula, I feed her on the same schedule and then offer her a bottle afterwards. She will breast feed for 35 minutes and then drink 1 to 2oz of formula.

Does this sound like a milk supply issue? Or my milk not having enough calories for her? I am also trying to pump as much as I can and usually end up giving her everything I pump in a bottle on the same day. Her pediatrician wants to get some weight on her and then says we can try and wean back off formula. I am worried she will become reliant on it or the bottle, and that my supply will decrease because of supplementing, even though I am trying to still breast feed as much as she wants and pump as much as I can.

Any suggestions or thoughts? I am just bummed because I wanted so badly to breast feed and now feel like I am not able to do so successfully.