How To Treat Bubbling Noise In Throat Of A Baby?

I have a 16 months old boy , 3months ago he has a cold after the cold he started making a bubbling like noise in his throat every time he gets upset and he tries to swallow saliva at the same time . Doctor gave me medicine for accident reflux but he has been taking it for a month and he still has that noise. I changed his diet and milk to lactose free too. You can see that it bothers him because he wants to cry .