Glad to be of help
It usually takes about 2 weeks for dairy to be out of your system, but can take up to 4 weeks. You should however start noticing a difference in the first week or so. If you want to have the best results you will have to be very careful as to what you eat, you will be shocked to see how much food products contain dairy, it is not only the obvious things that contain dairy. You will have to become one of those ladies that stand in the shopping aisle reading labels

Anything with the words "casein" or "lact-" in the ingredients list contain dairy.
You may want to switch the bottle of formula you give to a Hypoallergenic formula.
As to the oats, the results should be much quicker, about 2/3 days.
My LG was also on Nexium until she was about 5 months. It was the only thing that worked, provided we followed the instructions carefully, ie empty stomach and wait about 30mins before feed.
I would be careful with the Bennetts and try to limit its use as far as possible, I have heard it has negative side effects. On the other hand you don't want your LO to be suffering in pain. You can try Bonnycare (Dischem stocks it) as a natural alternative, but as with any herbal remedy it takes a few days to kick in. I have also heard that Colicalm is good, but I don't know where to buy that.