Weather today in the South East was wall to wall sunshine, temperature was about 17-18 although felt warmer in the sun.
Ground is still cold and there was a heavy dew.
Good conditions for thermals, you probably took off in the downside of a thermal and then ran into a series of thermals which makes for pretty uncomfortable flying in a light aircraft.
What was your IAS? I'd have probably tried fast cruise to give better control authority (and confidence), sounds like you were a little slow for the conditions.
I got caught out one late september back when they still burnt the stubble, very sunny day, light winds and stubble fires all over Cambridgeshire/Huntingdonshire. Very bumpy roller coaster which cost me an extra half hour cleaning the go faster streak from the passenger side.