Not gaining weight... ?

[Calluna]

It's not so much the actual number that's bothering me, more the fact that he's not gaining.

How many nappies should he have a day? Most days it's 4 to 6 wet (this concerns me a little) and 1 or 2 poos.
I try to give him water throughout the day but he mostly just spits it. He also has 4- 6 BF's a day.
He produces tears when he cries, has an abundance of syliva (lol), plenty of energy- although he still has 3 sleeps a day and can only manage 2hours between sleeps still.
He's been fluctuating between diarrhea and constipated the last week, but I think that he's teething?

He's due for a check up in the next couple of weeks so I'll talk to the doctor then but would like to hear your thoughts.