Maintaining Historical Data in a Current Data Base

Using Excel to calculate Net Worth every month. Most of the spreadsheets involved cover current month only and are replaced each month. However, I do include one sheet of historical data to plot major values over time. To do this, it is necessary to add a new column to the historical sheet each month while retaining all the previous columns. I don't know how to do this automatically.

Easy to pick up data for the current month in the historical sheet by establishing pointers in each cell in the last column. However, this data is then overwritten next month and the previous data are lost. If I could copy the last column of historical data each month to a copy inserted just before it without copying the source pointers too, this would work but I don't know how to do this.

Any suggestions? Thanks