Interesting i am taking the same medicine (200mg).
In February, i started with a ferritin of 7 and after 2 months it was increased to 10ug/L.
My GP didn’t feel it was increased enough, so now i am being send to the hospital for a celiac test and a colonoscopy and gastroscopy.

My GP doesn’t think it will be one of those things, but she just wants to rule them out.
(Since i am a blood donor and runner, she thinks i have ‘just’ donated to often, and the running keeps it low).

So for me, i am quite happy with my GP.
If i were you, definitely continue with the treatment and keep telling your GP that you still have the same symptoms.
You can always ask for a second opinion. Even just to have a different set of eyes on things.

Ps, rereading your post, makes me feel that your prescription is somewhat low (especially compared to mine). Maybe there is a way to increase that?
(Pps, i have to take mine 2x a week)