plottingissue

I want to plot the number of items in each quarter of the year. But the results are incorrect.
'incorrect'- There are more items in the earlier years plotted than later. Though analyzing the dataset it should be opposite.

df.head() 
        date       username
0 2007-08-09      ginaemiko
1 2007-07-30        AtomAnt
2 2008-07-08  RecoveryTweet
3 2008-07-05  RecoveryTweet
4 2008-06-29            lwu

ax=df.date.groupby([df.date.dt.year, df.date.dt.quarter]).count().plot(kind="bar")
ax.set_xlabel('Time (Year, Quarter)', fontsize=16)
ax.set_ylabel('Count', fontsize=16)
plt.tight_layout()	
plt.savefig('./plots/tweets_quarter.png',dpi=200)