grossly speaking, burn out usually happens either when we do something too much or when we get bored of it.
if it's the former, maybe consider slowing down? perhaps intersperse your training with other fun stuff?
if the latter, try reflecting on your (and/or dojo's) training style. too much emphasis on physical techniques? too much spirituality/philosophical talk? too much chatting? too rough? too soft? be aware of what you are doing and perhaps explore the other perspectives of aikido. hopefully your dojo/sensei would appreciate that, but if not, consider training at other dojos to get a fresh perspective. the world of aikido is just so so rich of possiblities.
if it feels like you're pushing against a brick wall, have you tried pulling it instead?