low weight gain

Jeremy has not put enough weight on to keep my piki te ora nurse happy. She did tell us not to worry too much but she seemed a bit concerned.
He is now 5.44 so has only put on .17 in two weeks and it should be twice that. He has grown 3.5cms though. Our nurse has recommended to use infant gaviscon to see if that can settle his vommiting but I can't decide if i want to put that into his system.
Has any of you used this before? If yes, please let me know if you found it helped and if you were worried about feeding a young baby something like this when their systems are still only really ready for milk? Or am I being silly about it and should just give it too him.
He is a very spilly baby, and vommits a lot but it doesn't hurt him when he does.
Anyhow, bit worried but trying not to be
Nurse is coming back next Fri to weigh him again.

Quite often when they grow upwards they have a steady weight (for that week) and gobble up in the following week. I think I'd be inclined to just keep an eye on it for the moment. (I haven't looked up to see where he would be sitting on a growth chart.) If he's super-spilly, is he perhaps overfeeding and then spitting it all back up?

Ben was the same, the plunket nurse suggested we took him to the doctor who suggested infant gaviscon, which was a load of rubbish as Ben was just gaining weight slowly and growing lenght ways quickly!!

Hes still got slow weight gain at 14mths, some babies just are slim and long ( wish I was!!) as long as hes drinking and eating ok and alert don't worry