Hooray! I hope the Mestinon helps.
When I first started to take Mestinon I didn't notice anything for about 4 or 5 days.
It took 5 months for Mestinon to do more than just minimize my symptoms (which was wonderful and I stopped getting new symptoms!). I think this was mostly due to me trying to get the dosage correct, but maybe it does take a while for Mestinon to help fully.
I did reach a maximum effectiveness for Mestinon after about 5 months.
Too much Mestinon is as bad if not worse than not enough so be careful and pay attention to your body.