P.G.
Get a lactation consultant. I got Shingles 3 days after giving birth and was told to pump & dump - GRRR. But got a lactation consultant to get me back on track. I don't know anything about this website - BUT it has a picture of the formula supplementing device that I used to make sure my son got what he needed from my breast (http://www.lowmilksupply.org/abs.shtml)
He sucked on my nipple, and the formula gave him whatever my breasts weren't capable of supplying. His sucking increased my supply naturally, and I was able to stop supplementing after a time - AND he didn't have to work super hard. As he got stronger, my supply got better and then it all worked.
But I needed the Lactation Consultant to do it. It should be covered by insurance because of your son's issues - I would ask and see if they can code it as medically necessary.
Good luck!