You know, some time ago we were discussing hip and joint pain and it seemed that a large number of us had it for some reason. I thought the extra calcium I was taking might be causing my bones to be sensitive, but I'm still taking calcium and my stomach's better and no more hip pain. I also changed my chair at work. That helped quite a bit initally, but I think maybe just getting my guts straightened back out got rid of the rest. Unfortunately, no one on here's figured out why so many people seem to have pains like that.
Can you use a heating pad or, at the very least, a hot water bottle at work? My first couple of plane trips overseas were agonizing; I have never had back problems, but mine sure hurt after 8-9 hours in coach. But my last trip I got one of those self-heating back wraps (get them at any pharmacy) and put it on for the duration and was like a normal human being when I got off the plane. I think it kept my muscles from "freezing up" as I sat upright for hours on end without moving.
Gas pains are also eased by heat, so I think if you could try something warm on your back and/or stomach, that might help you out at work. Other than that, try gas pills. I used to use the chewable kind because I could take them without water, but you may need something stronger; I think Gas-X has a new Advanced Strength version out that you may need. Also, if you have access to hot water at work, try making tea. Some of the other ladies on here are big herbal tea drinkers and they can tell you what to drink for gas (peppermint, I think) and what to drink for nausea (ginger, I think).