what should I do to get a replacement of my sticker from my license plate ? Should I go to the DMV ? I pay it already but It never came to my mail box and I have the receipt with me. I got pulled over by the officer because I need my sticker.

Go in person and they can check the status of it. If it's been more than 30 days from the date of issuance, DMV can reissue a sticker.

The fee to replace ypur lost stickers is $21.00 no matter what- if you moved, or if the dmv sent them to the wrong address, or if post office lost them- even if you have the receipt that you already paid...