I have written this a million times already, but:
after each practice session I make a short summary of what I have just learned/improved. There is always something. Could be a very, very small detail, but everything counts!
Lately I have begun to write this summary down in my journal as well. It is good to look at in periods of self-doubt. I normally get much happier when I see that I, actually, HAVE achieved something even on those days "nothing" seems to happen.
I also think I am a dreadfully slow learner and the physical condition of my hands prevents me from practicing as much as I want - and sometimes I also have too little time! - but when I look in my journal I realize that I am, nevertheless, doing my very best. I am also happy that I am an amateur, doing this for fun and for leisure, so I don't HAVE to push myself more than I already do.