Help extending code into loop

I have a column of data that is interspersed with blank rows signifying a new data group. I want to find the average of each range in the row between each break. The code I have pieced together so far does this perfectly for the first set of data, now I need to get it to loop so that I can average the next group of data below that (and below that, and..)

Sub Average_range()
Range("e3").Value = Application.WorksheetFunction.Average(Range("d3", ActiveSheet.Range("d3").End(xlDown)))
End Sub

So running down Column D I have:

A
A
A
A
A

B
B

C
C
C

etc.

I need to expand the code so that it not only gives me the average of A's but B's, C's, etc.

Thanks!