We dealt with the same - you are doing great! It is a really sucky situation. Our girl had to be taken back to the hospital daily and pricked for a week and a half. Try asking your ped about vitamin D drops as well and take babe outside. There is something called breastfeeding jaundice as well which keeps the jaundice around longer. We nursed as well. Keep doing what you’re doing!
If they did not send you home with a phototherapy light, no need to worry. Both of my kids had extremely high bilirubin after birth. I almost didn’t get to take my son home with me, and with my daughter, I had to stay an extra day in the hospital. Both of them came home on the light blanket for a week. It was an absolute nightmare, as you have to keep them on it 24/7 besides diaper changes. If you baby’s levels are dangerous, they will 100% call you in. I would just keep an eye on baby’s weight. If you feel like he’s losing more weight again, then call the hospital and talk to a nurse.
Windows have a uv protectant in them to not allow the rays to come through to help with jaundice anymore. (It's why you can't get sun burnt through a window and why the sunshine doesn't fade your carpets/furniture.) Take that baby all the way outside for some sunlight. It's starting to get nicer out, and even just his face getting some rays can help. Listen to your doctors advice, there is some reasearch showing that formula helps reduce jaundice(doesn't increase weight gain), but breastfeeding is going to protect your baby for life. Pump every time you offer formula if you desire to exclusively breastfeed once his levels go down. The phototherapy is really what's going to make a difference. <3 you clearly care about your baby and would never let anything happen to him, and you're already doing everything you can. Remind yourself of that when all the worries and fears hit you.