Don’t make the decision to quit on the bad days.
Every job is hard. And most days are going to be difficult. In most situations you're going to be pushed, called out, and challenged—that is, if you're engaged in something worthwhile.
Who knows, it might be worth sticking it out, see how you feel on the good days. Just know, there are much worse jobs out there.
But, it might be time to quit if:
1) On the best days (when everything goes reasonably well) you still feel underwhelmed, dissatisfied, and longing for a change/challenge.
2) You’ve been branded as being someone or something you’re not. Sure, you might have initially done this to yourself, but once you’ve been branded as something that you no longer identify with, it’s almost impossible to change that perception. In this particular instance, the time to look for a new job is when you don’t need one. And, in this case, the time to switch jobs is before it feels comfortable.