it is scary when that happens and I would probably call the ABA and check what they have to say. It could have just been the week that things dropped off a little and next week you will have a gain. Where the scales the same? maybe that can explain the difference?
I personally would try to see if he would take a dream feed, keeping in mind that it can unsettle some babies or maybe squeeze an extra feed in there somewhere. Does he take both breasts when he feeds? if he doesn't you could try and offer both breasts?

Oh those early months are hard and I do think from the sounds of things you are doing a really good job!!