I know that it's hard to see yourself making mistakes. That is something that all must deal with, and none of us enjoy it either. Some of us DO make more mistakes than the average person, but there are
a lot of variables when it comes to cause.
A BIG cause is stress though. When we're stressed (physically or emotionally), our brain has to work harder to keep us going. So, if we're sick or depressed, our brain is going to have to work a lot harder not to make mistakes. That is a simple fact. If we add in additional possible causes (you're frequently distracted; stoned; financially distraught; etc.) each of those factors add even more burden to the memory. Mj is well-known for causing some disruption to a person's memory.
Personally, I believe that should be a factor in one's consideration of using mj. Some people have great memories despite their usage of mj (my bf has an
excellent memory despite his strong usage)! However, I refuse to use mj because I know that
my memory is extremely weak as it is (due to a variety of physical and emotional factors). Mj is just not the right drug for me. Even though it's been approved to treat my physical condition ~ I know that I cannot do it, as it's usage would directly affect my emotional state. See what I mean? It's so complicated!
I hope that I haven't merely confused you. I can understand how frustrated you are with yourself ~ I often fight feelings like that towards myself. And that's what it often takes for me. Fighting those self-kicking thoughts and emotions. I also go to a therapist weekly, as well as take anti-depressants and anti-anxiety pills (to make the meds more effective). Coming onto PC, also helps me get through day to day. Yes (in case you're wondering), I do try to take life day by day because life changes SO fast. It really does! Appreciating each day, each moment, also helps me build an appreciation of the good things in life as well. Otherwise, it's just so easy for me to overlook those good parts & then I dwell on the negative. Ugh!
Hope that I've made some sense to you, and that you're starting to feel a little better... as you can see others do understand where you're coming from. And we do have sympathy for you.

Try to take it a little easier on yourself. You deserve it. Okay?
(((gentle hugs)))