Quoting Boobie On Demand:" Put him to breast as often as possible. You don't have to stop him, he'll know when he's done. Your breasts ... [snip!] ... to make more. As for the surplus you have, you can use that to finish his feedings if he isn't getting quite enough just yet."
all this! just feed on demand mama. as long as he's having wet diapers (minimum of 4-6 per day) and seems otherwise happy and satisfied, then he is getting enough. you don't need to supplement with the bottle or watch the clock. Just be aware that his breastfeeding habits may be different than the bottle feeding ones. he might want to nurse more often and may nurse only 2 minutes or might want 40 minutes. just follow his cues. I'd suggest just nursing off one side per feeding at first. if he nurses for at least 5-10 minutes and then unlatches on his own, you can offer the other side. he may or may not take it.
you can keep pumping if you like having the extra supply in the fridge, but if he's got a good latch and you are able to stay with him most of the time (not going to work, etc), then you shouldn't really NEED to pump. He's still young, so you're still making plenty of milk. The "decrease" you noticed could be a growth spurt on his part, where he is now drinking more milk or it could be your supply regulating a bit. nothing to be concerned about at this point. =D