I've been experiencing the same kind of thing - my videos last year raked in far more views in a shorter space of time than the ones I make now.
However, in your case I think it might simply be that one of your videos performed exceptionally well and you just got lucky in the beginning, so your latest videos appear to pale in comparison.
I wouldn't worry too much about it - just keep making content and eventually the views will come. You're doing great!