"Feeling let down"

My son has been in and out of the children's ward since his birth 6 months ago. Each time he has been diagnosed with bronchiolitis, given treatment and then discharged. At our last follow up appointment with the consultant, we were advised that he was being referred for further urgent tests and that we would receive a call or a letter with an appointment. This was 5 weeks ago. I chased this up last week as I hadn't heard anything, to discover that an appointment still hadn't been made. I was assured that they were going to make one then, but this still hasn't been done. My son was then seen by his health visitor last week (she has been great throughout all of this) to discover that his weight has tailed off again (he's never been on the centile chart so this is of significant concern) so she contacted the GP and they have put another referral back in to paediatrics. 

I do not know where to go from here. My son is not gaining weight, has had bronchiolitis 8 times now, pneumonia and has never been without a cough in his whole 6 months. We have tried going dairy free, tried top up bottles (which he is now refusing to take) and he is still unwell and still not gaining enough weight. He is definitely now classed as faltering growth yet still no one has been able to give an answer as to what is wrong with him and what I can do to help him. 

I am feeling so let down by the service as the consultant has been absolutely lovely, however none of the things discussed have been actioned so my son is getting more and more unwell. Where do I go from here to get the help that my son deserves?