I read you saying multiple times that you fear blockages.....Not that you are having them. I am wondering if you might be contributing to overall weakness and inability to focus because you are not eating enough.
Agreed with the above replies that it takes time to rebuild and there is learning curve. But not eating is not going to help, unless you actually are obstructed.
Increased frequency and gas can also be because you are not eating. The general guidance, especially in the beginning, is small/frequent meals and low fiber. Try individual foods at a time and introduce new things slowly. It is a process over months, not weeks.
As for shakes....those always cause my system distress no matter the brand. But everyone is different. For me, I keep foods simple and made at home as much as possible. I'd just try things in small amounts over a few days and see how it goes. Introduce one thing at a time over several days so you know which things work, and which may cause distress. But please do eat unless you are actually obstructed.
It does get better and the range of foods you can eat will expand. I struggled greatly in the first year and had to push food to gain strength....but I got there. It is now 29 years later and that early struggle is a distant memory.
Stay the course. You'll get there. So glad you are here asking questions.