It would be a lot easier if you could have all your data in a tabulat format, each month below the previos, but I guess that is not an option due to the data source?

Try this in B22, copied down and across...
=IFERROR(INDEX($A$12:$F$16,MATCH($A22,OFFSET($A$7,5,MATCH(B$19,$A$7:$F$7,0)-1,5,1),0),MATCH(B$19,$A$7:$F$7,0)+1),"")

I have used the ranges you provided, but you will probably need to adjust these for your real data