There are two possiblities here!
You could have been burning your melt for a long time and it may just be time to change to a new one. In that case, clean out your burner and pop a new melt on.
The other possibility is something ALOT of vendors suffer from (me included) nose blind! Yes, you read that right! I suffer from this quite a lot as I'm constantly making and testing lots of different fragrances. What normally tends to help me is a good long sniff of coffee beans (don't ask me why it works it just does). Or take a few minutes outside in the fresh air and take a few deep breaths through your nose before heading back indoors.