Abby,
I also find coffee more helpful than Mestinon for my symptoms currently. It hasn't always been this way, but I am now taking 1/8th of a Mestinon pill every day and a cup of coffee in the afternoons (or a cup of tea if my symptoms are only mild).
I prefer the coffee to Mestinon when my symptoms are mild. The Mestinon makes me feel horribly nervous.
I think it is the heat that reduces my symptoms somehow. When it gets cold again I expect that I will be back to taking more Mestinon and having lots of bad days.