Need help in trigger

Hi every body I need help to write a trigger …

I have 3 tables
items :
item_id (interger)
add_date :(data)
info : (blob)

totals_info :
used_total (int)
insert_date (date & time)
item_id (interger)

totals_of_used :
item_id (int)

now when add new totals_info
I need to update the totals_of_used to be the sum of this item within one month from the add_date for this item,
where the total_of_sum will start from 0 each month

my english is bad but hope you understand what I want

and I’ll be very thankfull for help

umm … is it doable or no… I start studying trigger. but I can’t find something do same as my case