Hypersensitive Stomach

I am still trying to figure out my stomach and I feel it has become hypersensitive. I changed my work schedule about a month ago. I was working 7:30am to 5pm. Now I am working 11am to 7pm. With this change my eating schedule also changed and that about killed my stomach. I am now dieting and have focused in on more protein less carbs but I feel like every time I eat something new or something I haven't had in awhile, an example is tuna fish or a bowl of cereal, it creates pain and I feel hard and bloated in the mid section of my stomach right above my belly button. Has anyone experienced this?