Replace Max function with countif function

[kelly mort]

Set Drng = Sheet1.Range("B2")
Set lrRng = Sheet1.Cells(.Rows.Count, Drng.Column).End(xlUp).Offset(1,0)
lrRng.Value = Application.Max(Range(Drng, lrRng.Offset(-1, 0)) + 1

I have column H that contain say x, y, z against the data. When I want to add new data to system, I will specify whether x, y or z from a combobox. And I want the numbering done to match each of the categories x, y or z. So if the last x is number 4 then the new takes number 5 etc. That's check from the combobox then compare from the database and do the numbering.

I am thinking countif can do but I am stacked with the implementation.

I need assistance fix it.