DAX question - FX calculation aggregated

Hi!

I am new to DAX(M) and PowerBI and would very much appreciate if someone could guide me in the right direction for the following issue:

1. I have 3 different General Ledgers with 3 different Currencies, 

2. I have another table with the currency exchange rates per month.

3. I have a date table.

All the tables have been normalized and set up with correct connections/relations

My task is to create a measure that would show the aggregated sum of the converted amounts. 

If I show the values per say February, the measure would show the sums of [J(anuary * FX Jan) + (February * FX Feb)]

I realize that i could add a calculated columns to all the GeneralLedgers per month and multiply the sums with that months exchange rate and then to a simple calculate(sum)) function for the measure.

I am looking for a cleaner solution only using a measure to do the job!

Any hint of what to do would be very helpful! 

Thanks!