AOB9,
I know how you feel, as I have the same issues - sometimes its a month between lessons - last winter it was two months! If its any help I spent many lessons circuit bashing before I finally went solo after 27hours - one thing because I was being thick (!!) the other because of lack of continuity. Everyone tells me that continuity and practise is what I need to progress, and I believe them!
I'm hoping at some point to go down the route of taking time off work and cracking on when there is a week of good week of weather.
Frustrating isn't it...but I just try and be pragmatic about it and study when I can't go flying instead!