I'm not an expert, but by fussing, do you mean screaming / crying, or just grunting and making noises? I'm asking only because my LO has reflux and he grunts and groans in patches throughout the night as he goes in and out of sleep cycles. I kept him in my room for the first 5 weeks and finally moved him to his own room because he made so much noise that I couldn't sleep. I now keep a baby monitor in my room turned on low so I can only hear the loudest noises.
When do you give him Ranitidine? If he is crying and then refusing food, it may be that his reflux is not being treated correctly. Babies need 2-3 doses of it a day, they become tolerant of it very quickly, and it is related to their weight, so the baby must be frequently weighed and re-prescribed by the pediatrician. Here is a page I go visit all the time:
http://www.refluxrebels.com/Acid_reflux/Acid_reflux_medication.html The whole site is a good one, but this page explains the different medications.
My LO started on an H2 medication and moved to a PPI. If your pediatrician suggests you move to a PPI, do NOT let them talk you into using a compounded liquid form or a solution. Most of these, even the kits, go bad after 2 weeks, making you think it isn't working when LO gets symptoms at night.
It took me a while to learn my baby's different cries. We had a LOT of acid-reflux cries at night. They usually included a monotone crying in his sleep that would peak with a kind of high-pitched pain squeal. Babies with reflux tend to want to soothe themselves with a little bit of milk to get the reflux burn down.
My pediatrician ok'ed my baby sleeping on his stomach (I did buy LO a breath monitor because of increased SIDS risk). Babies have a deeper sleep on their stomachs, and as the physician's assistant told me, "The kindest thing you can do for a refluxing baby is get him off his back and onto his belly at night." It's not for everyone, and one should definitely discuss with pediatrician about this.
Also, reflux babies may refuse to eat if they associate certain feed times with pain.
My child is adopted, so I am not familiar with the logistics of breast-feeding, but could it be your milk supply is lower at night? Perhaps he needs a bit more? (this is absolutely a guess, as I really don't know)
I hope you get some answers and some sleep!