Most specifically, Shyvana, Udyr, Yi. Seems like I can't keep up with them in farm ever, they counter jungle me and I cannot fight them, and late game I don't have the damage to burst them down. Is 
just bad against these champs or am I not taking advantage of them/being aggressive enough?
Devourer champions are arguably easier to play against as they kinda have a time limit until they become useful. Taking scuttles (which offer 2 devourer charges as opposed to one), taking control of dragons, and invading their jungle/warding their buffs is one of the best counters, as a non-sated devourer is pretty underwhelming especially in ganks.
as nidalee you should just be living in there jung especially pre-6 because you can easily out duel them
