If he's refusing to nurse, then he is having a case of nipple confusion. You need to stop offering bottles to him. If you must supplement, use a cup, dropper, or finger feeder instead. ALWAYS offer the breast at feeding times, and comfort nurse when he's not hungry, but it will get him on the breast to help stimulate nursing.
Alot of moms think they are losing their milk supply when thats not hte case. Most breastfed babies don't gain weight as fast as they did from birth, around 3mos that growth slows and most doctors use the growth chart for formula fed babies (its likely put out by Similac or Enfamil). Ask your doctor to use or print out a copy yourself of the WHO chart for breastfed babies. Its MUCH more accurate. Also around 3mos is when your milk really settles into pace and you stop overproducing and only make what your baby needs which causes moms to think their supply is gone because they no longer feel full.
Nurse, even if he fusses, take a small break, then offer the breast again. He will need to relearn that he needs to nurse to eat, no more bottles. He will fuss because nursing takes work, and a bottle basically squirts the milk into his mouth and he just has to swallow with not much effort.
Also, your baby will hit numerous growth spurts over the next year. he will want to nurse almost constantly around 4mos, the 4mo growth spurt is the longest, most trying, growth spurt. MANY moms think they aren't making enough milk and start giving formula. Because the baby wants to nurse all the time, they wrongly think they aren't making enough milk because baby is wanting to nurse all the time.
Your milk supply will come back, you just have to take a 'nursing vacation'. Meaning you nurse round the clock every hour or so until your milk supply is up and your baby is taking the breast willingly and eating fully.
You can pump,which will help, but you HAVE TO REMEMBER that a pump will not pump out as much milk as your breasts have. So if you pump 2oz, that doesn't mean thast all thats there. Your baby can nurse out 2, 3, 4 oz or more than any pump can. But pumping will give you stimulation when your baby isn't nursing, and thats a good thing. You just have to remember that not pumping much is no indication of your supply. I think thats another thing that makes alot of moms stop nursing, they pump a small amount and think they aren't producing.