G.K.
You needn't be concerned that his eating around the clock is going to cause your supply to drop. Quite the opposite, in fact!! Milk supply is all about supply & demand, so the more milk your son is drinking, the more milk your body produces, and it only takes 2-3 days to increase or decrease your supply. So, if your son is nursing what feels like constantly, he could be going through a growth spurt and is doing what he can to help you make more milk.
Also try to keep in mind that your son is more efficient at milk extraction than ANY pump you can use!! Rest assured that he's more than likely getting a lot more than the 3oz you're able to pump. And I know that sleep is challenging right now, but the more (and better) sleep you get, the more milk you'll make :) Stress will also decrease your supply, just as your digestion is interrupted when you're upset.
As frustrating as it is in the moment, try to stick it out. My son was a horrible sleeper, too, and I hate to say this, but the only thing that helped him sleep longer at night was getting older. He FINALLY started sleeping longer than 4-5 hours when he turned 18 months old (and moved to Cali), and now that we have a new baby (5wks), he's not sleeping again *sigh*
As for supplementing with formula, keep trying. If he refuses the bottle, it could be because of a few things. The first reason could be he's not hungry. The second could be he doesn't like the bottle (most breastfed babies prefer mom). The third reason could be he just doesn't like the formula you're trying to give him. Try different formulas, different nipples (the bottle part doesn't make much difference), etc until you find something that works for you and your son.
Keep the faith: things will work out!!!