Have been looking at it, its not easy to gain much of a prediction for my area though due to the few low number of NB applicants on here. There is one for the month after me and a couple from a few months before and thats it.It's not just you. I'm in the same boat (application sent middle of March/2018).
Please, see the spreadsheet ...
and you will see that a lot of people are still waiting for the test letter...
Everything depends of your region/location...