Heather, first of all.

He won't dehydrate if you continue to offer him a feed. 5 mins if plenty of time for him to drink his fill now, and he is probably biting out of frustration and once he's satisfied his thirst/hunger. Keep the bfs short and if you notice that his sucking is starting to let up, take him off before he can bite and distract him with something else.

Another thing that might work is to switch holds on him. So if he's normally held in a cradle position, try the football hold. Make sure your attachment is spot on. Or try marcellus's suggestion to bf lying down. You might also like to try to limit distraction for him, so that he's not trying to pull off and look around. So go for a quiet, darkened room.

GL hun, I'd suggest calling the ABA too, 1800 mum 2 mum. You'll get another mum who's probably BTDT and it won't be as daunting as you imagine.