We've been pretty successful at BFing minus my sometimes not being able to pump as much as LO drinks while I'm at work.  Lately he is starting to fight the boob in the evenings.  (Morning feed is great.)  He'll nurse like normal for a few minutes (anywhere from 8-15 min) and then pull off, latch on, pull off, latch on etc while fussing.  We've started supplementing 4oz formula when he does this and I pump to make up for it.
I don't think it's a supply issue bc when I pump after he does this, I still get *some* milk.  Not overflowing bottles, but I know I'm not dry.  Is it possibly that he's tired and doesn't want to work for another letdown?  I have preemie nipples on our Dr Browns bottles so he still has to work to eat but I think maybe he prefers instant milk with bottles as opposed to having to wait for let downs.
Anyone else seen this?                 
                             
        
Re: any other BF babies boycotting the boob?
My Ovulation Chart
You can also try to manually express a little before nursing so LO gets instant gratification if it's due to impatience.
Good luck!