Trying to find a value, if not find first empty cell

I have a workbook I'm working on for our IT inventory.
I need it to look for the value of ItemName. If it finds it, move one cell to the right and add the value entered by the user to the existing value in that cell.
If it doesn't find an equal value for ItemName, I need it to find the first empty cell in column A, then input all 3 values entered by the user:
ItemName
Qty
Location

I can't get it to go past looking for a duplicate ItemName.
Link to download the file:
Here

Option Explicit


'Define variables
Dim ItemName As String
Dim Qty As String
Dim Location As String
Dim ExistQty
Dim r As Long


'Initialize UserForm and calls to Subs
Private Sub UserForm_Initialize()
    Call ComboBox1_Change
    Call ComboBox2_Change
    Call ComboBox3_Change
End Sub


'Submit data gathered to inventory
Private Sub CommandButton1_Click()
    Worksheets("Data Entry").Activate
    Range("A2").Activate
    Do While IsEmpty(ActiveCell) = False
        If ActiveCell = ItemName Then
            ActiveCell.Offset(0, 1).Select
            ExistQty = ActiveCell
            ActiveCell = Qty + ExistQty
            GoTo LastLine
        Else
        Do Until IsEmpty(ActiveCell) = True
            Worksheets("Data Entry").Activate
            Range("A2").Activate
            ActiveCell.Offset(1, 0).Select
            r = r + 1
            GoTo NextLine
        Loop
        End If
    Loop
NextLine:
    Worksheets("Data Entry").Activate
    ActiveCell.Value = ItemName
    Worksheets("Data Entry").Activate
    ActiveCell.Offset(0, 1).Activate
    ActiveCell.Value = Qty
    Worksheets("Data Entry").Activate
    ActiveCell.Offset(0, 1).Activate
    ActiveCell.Value = Location
    Worksheets("Data Entry").Activate
    ActiveCell.Offset(1, -2).Activate
LastLine:
    Worksheets("Main").Activate
End Sub


'Cancel button to end process
Private Sub CancelButton_Click()
    Unload Me
    Worksheets("Main").Activate
End Sub


'Drop down for Item Name
Private Sub ComboBox1_Change()
    Worksheets("Totals").Activate
    With Worksheets("Totals").Range("A1").CurrentRegion
        ComboBox1.ColumnCount = 1
        ComboBox1.ColumnHeads = False
        ComboBox1.RowSource = .Offset(1, 0). _
        Resize(.Rows.Count, .Columns.Count).Address
    End With
    ItemName = Me.ComboBox1.Value
End Sub


'Drop down for Location
Private Sub ComboBox2_Change()
    Worksheets("Quantity").Activate
    With Worksheets("Quantity").Range("A1").CurrentRegion
        ComboBox2.ColumnCount = 1
        ComboBox2.ColumnHeads = False
        ComboBox2.RowSource = .Offset(1, 0). _
        Resize(.Rows.Count, .Columns.Count).Address
    End With
    Qty = Me.ComboBox2.Value
End Sub


'Drop down for Quantity
Private Sub ComboBox3_Change()
    Worksheets("Location").Activate
    With Worksheets("Location").Range("A1").CurrentRegion
        ComboBox3.ColumnCount = 1
        ComboBox3.ColumnHeads = False
        ComboBox3.RowSource = .Offset(1, 0). _
        Resize(.Rows.Count, .Columns.Count).Address
    End With
    Location = Me.ComboBox3.Value
    Worksheets("Data Entry").Activate
End Sub