How do I sum data by month/YYYY in VB code in VS2010?

Hello:

I would like to sum the total of several columns by each month based upon a user selected date range.  

This is what I have so far:

HERE I GRAB ALL THE DATES AVAILABLE IN THE DATE RANGE
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Dim dateList = From id In wellData.tblBWgallons _
                         Where id.InputDate >= CDate(pckrStartDate.Text) _
                         AndAlso id.InputDate <= CDate(pckrEndDate.Text) _
                         AndAlso id.Cumulative > 0 _
                         Order By id.InputDate Ascending _
                         Select id.InputDate

HERE I MAKE A LIST  BY M/YYYY
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        Dim MonthList As New List(Of String)

        For Each m As Date In dateList
            Dim mon As String = CStr(m.Month)
            Dim YY As String = CStr(m.Year)
            Dim DateName As String = mon & "/" & YY

            If Not MonthList.Contains(DateName) Then
                MonthList.Add(DateName)
            Else
                'do nothing
            End If
        Next

PROBLEM AREA - I CAN'T FIGURE OUT HOW TO GRAB THE DATA BY THE LIST
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        For Each rec In MonthList
            Dim mmyy As String = rec  (EXAMPLE mmyy would be 3/2010)

            Dim getRecords = Aggregate id In wellData.tblBWgallons _
                             Where CDate(id.InputDate.Value.ToString("m/yyyy")) = mmyy _
                             Into Sum(id.Cumulative)

        Next

Any help would be most appreciated!