Compare data for current and previous months

Looking for suggestions on how to achieve following:

I have a simple report that summarizes citizens requests submitted to the City. The report is ran at the end of the month to get a summary of all request types and counts. I would like to enhance the report and also include the summary of reports from "last" and calculate '% increase/decrease' in all the report types.

I tried a few things but cannot figure out how to get the data for the 'LastMonth'?  

Appreciated any and all suggestions.

Thanks,

Nataliya