Hi D.-
Breastmilk last for 3 months in the freezer. I would definitely continute to feed that to your son a little because it IS better for him... but you know, don't feel guilty if you have to supplement with a little formula!! As long as he continues to get some breastmilk, even if only once or twice a day, he'll still be getting all the benefits of breastmilk (the antibodies, emotional security, etc...).
Believe it or not, you may be producing plenty of breastmilk for him. As your son gets older, your breastmilk changes. It becomes thicker, heavier, and more fatty... therefore you may not produce as much, but it's actually more filling. Three ounces every two hours is actually close to what I get a lot of the time and my daughter is 7 months old! Trust me, your probably producing plenty for him! Breastmilk works on a supply and demand system... the more you nurse, the more you will produce. You could also try eating oatmeal every morning. A friend of mine who's a lactation consultant gave me that advice.
If you're still worried you're not producing enough, you could also mix some of your pumped milk with some formula. That's supposed to help them digest the formula and give them a more familiar taste if they don't like the formula.
I hope this helps!