OP, I wouldn't worry too much. While your renewal is taking longer than average, there are always outliers. One option is contact your Congressperson or Senator (assuming they are immigrant friendly) to inquire on your behalf.
__________________
Initial Approval: 11/13/12
1st Renewal: 10-7-14
2nd Renewal: 10/12/16
3rd Renewal: 5/16/2018