dwindling supply 😫

Ash
Hi ladies,
  So I have a 4 week old and have been exclusively bf up until now. He lost a lot of weight after birth and was having a hard time gaining it back so the dr told us to supplement with formula twice a day. He's gained weight which is great. However, my milk supply is suffering. I pump when he gets the bottle from my husband and I'm between every feeding, but still I am starting to get less and less milk each time. My baby has an indent in his upper palate at the roof of his mouth and a slight lip tie, so his suction is not very strong, which is why he wasn't getting enough from just me. Bc his suction is weak my supply and demand isn't strong. And even though I pump, a baby's suction is what increases you'd supply most. I don't know what to do. 😫