I have had "IBS" for at least 20 years now and I am still sometimes sick because of it. I have had symptoms like yours as well. Nexium can also cause/aggravate diarrhea. I needed acid reducers too, but had to use less potent ones (pepcid AC) because they did not cause the side effects Nexium did for me. Some foods were a problem with me, so I used an elimination diet to identify some of them. That was after the 1st endoscopy. Have had 3 of those and 2 colonoscopies. All "normal". Saw an herbalist. She gave me an herbal formula that helps calm the digestive tract and restore the mucus membrane. It helps a bit.
Follow up with your Dr, get the tests done to rule out anything else! If they diagnose you with IBS you will have a lot of work to do keeping track of what you eat, how you feel. Stress is a big component!! Exercise is key for me. I try to do some at least 5 times of a week. Recently I went away to visit my kids/grandkids and now I am sick again. The stress of the airplane trip, eating out a lot at places that may not have understood my food allergies, and lack of exercise put me on the couch again! This time no pain but the spasms, gas, bloating are so bad, I feel terrible. My gut feels like a giant water ballon. Heat (a rice bag warmed) also helps me some, relaxes my gut. Camomile tea is good too. With time, rest, and my regular diet I should improve again. Try not to worry too much. IBS is different for each person, and even changes at times in each individual. This is the kind of condition you really have to do your homework, study your body, keep a journal and figure out what sets you off. Try also to see if gluten/dairy could be culprits. Most of all, be grateful. Take deep breaths and find things to be thankful for. If it is IBS at least it is not cancer or Crohns! Praying for you! Go back and see your Doctor for a definitive diagnosis!