material change price

hi all.

im facing a problem related to montly price.

i have to get the details material, plant, val class, mrp controller, profit center and 12 months price with respect to period.

i m giving the selecion screen values as 09.2005 09.2006(spmon).

i have to calculate price for 12 months (mbewh-verpr)

im passing the values to fieldcat with respect to the given period.

but im getting nil values in field cat.

how to convert the period and get the values corresponding to montly price.

also we have to check mbewh-lfmon(month) and mbewh-lfgja(year).

plz give logic or code.