17 week old not drinking

[Jessicacacaca]

I have a 17 week old boy that has been formula fed since birth, we had some issues with his formula to begin with but he is settled on a comfort milk.
The past 2 weeks he has been drinking 2oz from his bottle and then crying/screaming and pushing the bottle around with his tongue or biting it.
If I offer his dummy he takes it straight away making his hungry noise and happily sucks on it. I've tried different teats and different bottles all together.
He started teething quite early but none have come through yet, I'm fairly certain that it's his teeth bothering him. I took him to the doctor a week ago just to check there was nothing wrong and the HV offered no help even though he's dropped to the 25th centile .
I've tried teething gel, granules and calpol if he's really bad.
Does anybody have an idea of how to get milk into him? I'm at my wits end with it and worried he's not drinking enough.

I have a thread describing the exact same behaviour on the Allergies board (my DS has CMPA)
My 17 week old DS is doing the same thing. Occasionally takes 3oz, but most of the time will only take 2-2.5oz then refuse any more.
I've read that a baby needs 2-3oz per lb of body weight in 24hrs. So if my son was drinking the minimum 2oz per lb, then he would need 24oz in 24hrs minimum - and he's having nowhere near that. I keep trying to tell myself that if he wasn't having enough, then he wouldn't be happy and satisfied between feeds and wouldn't be sleeping? We are under a dietician due to his allergy and she's on my back about his weight as it is so I'm worrying

What happens if you use teething gel or Calpol? Btw if it is dental, ibuprofen is much better than paracetamol.

Is he unsettled at any other time?