Unfortunately. our bodies are not consistent.
I find days when my BG just seems to feel like it needs to do its own thing. This may go on for a week or so.
Like you, I change my insulins and change my pens and it does seem to make any difference. Then I up my insulin because I think I may be going down with something. This works for a few days and then, with no sign of the "something I was going down with", my BG plummets and I am back to normality.
I admire anyone who has a consistent BG all the time and lives what I would consider a "normal" life.
As frustrating as it is, I would continue doing as you are and reacting to your BG changes. Try not to get stressed by it (yeah right?). And test much much more than usual. If you can get one, a Libre may help.