The easiest way to do this is to use a helper column. Sort your data in Col A (data Sheet) so that the replications are next to each other.
Then insert a couple of columns before A.
In what is now Col B insert
=If(c2=c2,max($c$1:c2)+1,1)
Then in what is now col A simply join B&C
=b2&c2
This will give you a unique ref for each entry and then from this you can use your vlookup to search this unique ref to get the answers you need.

If you need a bit more help post an example and I will make it work for you

Matthew