Nexus 7 charges very slowly, even with 2 amp chargers
Two things to consider:

1 Depending on the charger, the Nexus might not recognize it as a 2A charger. It does not actually measure its capacity, but relies on some properties of the otherwise unused data-lines of the USB connection to the charger. Shouldn't be the problem if you used the charger that came with the Nexus.

2 It is possible that the Nexus is confused about the actual state of the battery. This can be re-calibrated, but is a rather involved process - especially if you don't have root on the device yet. However, guides can be easily found with Google.

Where does this leave you:


If you haven't used the charger that came with the Nexus, do so and see if problems persist.
If the charger is not the problem and you still have warranty send the device in.
If you are out of warranty try recalibrating the battery stats.