We're now 5 weeks on from my initial posting and I thought I'd come back to you with some feedback from all your valuable advice.
Thank you to all of you, we really seem to have the situation under control now. We have continued with the Ranitidine, the head of DS' cot is elevated, I am avoiding all dairy and am block feeding as well as keeping DS upright for a minimum lof 30 mins after each and every feed (I have tried to cut corners a couple of times on keeping DS upright for such a long time but she ends up vomiting and is clearly uncomfortable - if 30 mins is the 'price' I need to pay, it's certainly worth it).
Within 24 hours I felt that I had a new baby, or should I say the happy go lucky baby I had before. DS still suffers from the occasional fussy and gassy sessions but she's certainly not in pain as she was before. Thank you to all of you who offered your support.