My hope is you have seen or talked with your doctor. Hopefully you are getting some relief. Not to presume to advise, but with the nebulous nature of your pain, if I couldn't be seen, I would be asking for something to address the pain. Untreated pain is not something you can endure without consequences. Like any other CF issue, the effect is cumulative.
I used to take Celebrex. If you have problems with ibuprofen, chances are very good that Celebrex is not going to be any better. Also an NSAID, it's side effects are proportionally stronger (worse) as is the benefit. An antiinflammatory drug probably won't improve the pain you describe if my suspicions are correct. (Stylecomfy, I had been working on this post when you added your contribution, I don't mean to be redundant).
Triples15 has listed the same conditions and the most revealing tests I would have. Keep in mind that every illustration of the abdominal structures paints the transverse colon, much lower than it actually fits, to illustrate the organs behind it. The transverse colon fits against and up under the front ribcage, wedged against the liver and a bit of the diaphragm. Your stomach is quite a ways up into the rib cage, the upper stomach is even with the bottom of the left pectoral muscle.
My interest is the junction of the esophagus and diaphragm. This is the Grand Central Terminal for many organs and organ systems. The splanchnic nerves nerves erupt through the vertebrae in the neck and travel along the "oral process", from the mouth on either side of the esophagus down through the diaphragm, wrapped around the stomach and intestines. They wad up just below the diaphragm as do huge veins and arteries, making it one of the most anatomically congested areas in the body.
These powerful nerves enervate the stomach and most of the abdomen. What is commonly known as the "solar plexus" is technically the celiac plexus. This "ganglion" provides the coordinating operations of digestion or liver functions, releasing the brain to perform more important functions. That is until something like a stuck gallstone sends relatively peaceful nerves into a panic. Unfortunately the mysterious and hard to pronounce splanchnic nerves are more accustomed to giving orders, making nonsense out of incoming signals, not so much. In other words your brain doesn't receive a signal that seems to relate to the gallbladder, pancreas, liver and such. The possibility of a bile stone, a gallstone assuming that you have a gallbladder, can produce exquisite epigastric pain. Sometimes it takes on the tone of a seriously sour stomach, heartburn or a stuck bit of air, a burp that really hurts. Both pancreatitis and a gallbladder attack can give you a higher back ache. But all of this is on the left side.
Pain on the left side could be a pleural effusion. Sort of like what the doctors are saying except for what's rubbing, and where. I've had pleural effusion on the left side a few times. It's been painful and virtually painless, depending on the episode. The latter has a gurgling sensation associated with it and for me at least I'm going to be hocking up a hemoptysis in the very near future. Pleural effusion is an infection between the pleural membranes. Depending on the type of infection, the membranes tend to adhere or slip easily past each other. If the infection is affecting both membranes at the same spot, adhesions and painful rubbing goes on.
The painless pleural effusions I have had began as abdominal infections, pancreatitis one time and a common theme amongst CFers, diverticulosis, turned diverticulitis, on a couple of occasions. The latter of my painless bouts of pleural effusion describe the closest thing to your painful experience.
You mentioned that you have been sick, not eating a lot and very likely, not drinking water and electrolytes in adequate quantity. Our transverse colon tucks tightly into the upper quadrants of the abdomen and few areas of the colon are more vulnerable to the stress of whatever food is turning around the corner. If you are a bit constipated, okay, a bit more than usual, coughing, straining on the toilet and just being sick could cause a flare up of a diverticulitis. Even a single eruption could be quite painful, possibly excruciating. If this is the case, antibiotics fit the bill, sorry.
Hope you feel better soon,
LL
In my case the pancreatitis was always easy to diagnose with a blood test of my amylase and lipase levels. Then a few years ago I started have a pain that felt VERY similar to pancreatitis, in fact, I was sure it was pancreatitis, but blood tests showed it was not. An ultrasound showed thickening of the wall of my gall bladder and sludge in the duct, but no actual stones. They followed the ultrasound up with a HIDA scan that showed my gall bladder is almost non-functioning. They started me on Actigall and recommended removing the gall bladder. Luckily enough the Actigall did the trick and I have not had the pain return so have not had it removed. Fingers crossed.