It is uncommon but not unheard of. I am in a little bit of the same situation since I started plying NL50 in August. Over 16,000 hands I am running about 14 buy-ins below EV, and in September alone I have run nearly 17 buy-ins below EV. Every time I think things seem to be changing it goes for a **** again - twice in the last few days I got a guy all-in post-flop with 80%+ equity only to lose on the river.
Honestly, I'd rather just get it in bad and know that I screwed up than constantly making good decisions that lose me money. I am running 12+ bb/100 but have nothing to show for it - I want to try moving up in stakes but I can't do it when my bankroll is never growing.
Here are my graphs for August-September and for September just to make you feel better that you're not alone here.