@WorriedGuy123 you are not going to die, calm down. Gut issues are terrific to handle but you just have to understand them first and what is causing them before you know what to do. My advice is that you are wasting time with western medicine doctors. They will find nothing on your colon and they cant do nothing.
Your digestion system is messed up the same way like many of us here. So there are many reasons why this imbalance occurs after finasteride use. You have to support the system the best you can when you are going through the worse. For undigested food you can consider trying HCL and good quality enzyme on both bigger meals and try if it can help. Those two will help your body to break down the food you eat and get the nutrients your body needs now when its not in order. Do your research before you try anything. You have to understand what you are doing before you take any supps and have to understand what the supp is doing.
Also find a good experienced nutritionist who knows gut issues and get tested for SIBO and work your gut with your nutritionst. I would but a little bet in that you have SIBO and it would be interesting to know if you have it.
Other things, eat your food warm, eat cooked vegetables and chicken/fish/soups which is easy for the digestion system to handle. Also drink your water room temperature. Warm because your body doesnt need to waste energy to heat up the food.