Once again, post hoc ergo propter hoc is a logical fallacy. You gained 15 pounds. It doesn’t logically follow that the shot caused you to gain 15 pounds.Theres also first hand experience. The Johnson and Johnson shot made me gain 15 pounds.
First hand experience is just another way of saying limited observation or anecdotal experience. Again, there’s a very good reason why we do not rely on it and instead rely on randomized clinical trials. Because, as you have so effectively demonstrated to us, people cannot avoid logical fallacies in their recollections. RCTs eliminate as many sources of bias as possible.