I think it isn't easy to create a metric like this. the problem is that the dimension used as rows filters the data and does not allow to check outside...
I once saw a possible way to go but can't find it anymore. however, maybe you can use some fancy "cumulative sum" (where you look back for the last x month) and segments for last/previous month to find out in what month you might be.
One idea: why don't you use the dimension "month of year" which would allow to check data (month) of "last year" to figure out in which row you are. the display something based on current year. to achieve this, you need to have full data of last 2 years in the table (or in the metric)... never tried it but might work