I evolved my weepinbell at level 24 into a victreebel but it is now level 37 and still hasn't learnt any new moves?
I'm not sure what game you have, but most of the early pokemon that evolve by stones typically don't learn many moves by leveling up, which is why it's a good idea to grab the moves you want first. In Gen IV, Victreebel won't learn another move until level 47, so there's nothing wrong with him.
Victreebel learns moves at Level 47 in in Gen 4 and 5. It doesn't learn any moves in Gen 1, 2 , or 3 by Level Up.
