Both mean different and I'm not sure you are looking for that.
I have read three books this month - the process is finished. You are done with those books in this month.
I'm reading three books this month - You are reading three books simultaneously in this month OR You plan to read them (and are sure).
I have read three books (in) this month - The last three books of HP series.
I'm preparing for the civil service exams and reading three books this month (The General Knowledge Book, the Aptitude Book and Book for Reasoning) OR I am pretty confirmed to read those three books this month as I have an entrance exam of Civil Services. [You use present perfect for the future if things are sure - The train is leaving in 10 minutes].
So, if you want to mean that you are reading those books in pipeline, you may simply say:
I plan to read three books this week/month/year
Or, as I said, if you are pretty confident and the thing is sure,
I'm reading (will read) three books this week/month/year.