Formula needed lookup and sum across multiple tabs

Hello All,
I'm in desperate need of some help simplifying a strung together vlookup statement.
On the attached, on the "Total" tab, you will see in column "A" there is a concatenate of a few fields I used as my "lookup_value" in my vlookup statement in column "O".
I used a concatenate field in all the other workbooks to find a total for each field in column "A". Although my vlookup formula in column O works, I'm looking for a more dynamic solution so when the next month's data (April 2018) is added to the other workbooks, I will not need to manually change my LONG vlookup statement. Is there a better way to write this formula?
I believe the figures in column O are correct so you can use that to test.

Any and all help is greatly appreciated!

Regards,
Andrew

This is excellent, Shukla!
one quick question - I see you are referencing Q7, which is the tab name. I was thinking of adding another sheet with just the tab names in a table format - let's say "sheet 5" from cells A1:A7. How could I adjust your formula to not reference Q7 instead it'll reference the table on sheet 5.

thanks1