Struggling with Digestive Issues

Does anyone else's digestive issues have almost nothing to do with what foods you eat specifically? It doesn't really matter what I eat for the most part, I end up with immediate abdominal swelling and fullness. I always end up so backed up as well, no matter what I eat. I can drink tons of water and eat soft, fibrous foods and it won't make a single difference. the funny thing is though, the only foods that actually pass through a little faster and cause less swelling and bloating are.. refined and sugary foods like cake or donuts. i once ate nothing but cake for 3 days (it was a really good cake lol) and I was doing better than usual and I could eat more while being less bloated. aside from that, just.. anything going into my digestive system causes problems, even drinking water. it's so annoying, because it's impossible to avoid just by eating certain foods or something. and since I get so full after small amounts, a meal for me is like a piece of toast or something, or a cup of soup, so it's hard to maintain my weight sometimes, and even when I'm hungry I'm still full and bloated. it's a constant struggle