After I switched to vegetarian diet I have not noticed _any_ difference in brain/personality/iq, I ve just lost extra weight.
And have less allergies.
Aside from that - nothing.
I've seen claims that it is hard to notice how/when your intelligence changes over time. A friend who had some health issues for a while (sorry, I'm not giving more details) played (simple) computer games quite a lot, because the results showed functionality trends.
ymmv, of course, but if I were you I'd play a few games like that over time while trying creatine supplements. If they help, I'd continue.
There were mostly FB-games. Things like "Who Has the Biggest Brain", word games (speed reactions), like Word Drop and Word Challenge in FB.
(I don't know anything about these games; I just have their names and a datapoint that they were good to verify daily shape and trace mind effects for medicines, etc. For some specific problems I'm not going to discuss.)
It seems there were two ideas here. One, do the stupid game enough so you didn't learn much by doing half an hour again == that is, it was a good test of present ability. Two, find something that is relevant for the problem you have.