Can't put my 8 weeks son on feeding schedule. Help!?

I've been trying to put my 8 weeks son on feeding schedule for the past week but it seems impossible. He's both fed and bottle fed (pumped out milk and formula) but mostly on bottle (I only feed him twice a day.) I tried to feed him every 3hrs and about 3 oz each time, but so far, he has been unable to keep that schedule. Sometimes he can only take in 2 oz, sometimes he seems to be able to have more than 3 oz. Many times he needs to eat 1 hr after I just fed him. It's like the only time I can get him to wait more than 3 hrs to eat is when he's taking a nap. I am careful about reading his cues to make sure I do not interpret tiredness with hunger. I also use pacifiers to stretch out the time, but most of the time it doesn't work. After 10 min or so, he spits out the pacifier. It's driving me crazy with about 12 times of feeding per day... Does anyone have suggestions? Thanks!