Note this answer is wrong - see @crop1645's comment; I've left it in case it is of use referenced from someone else's answer.
Roll-up summaries do support some basic filtering as shown in the screen shot below. (The relationship between
Information has to be master-detail.)
But formula fields are not available in the list of fields offered, so instead of being able to just add a checkbox formula field called e.g.
MONTH(DueDate__c) == MONTH(TODAY()) && YEAR(DueDate__c) == YEAR(TODAY())
for use as the filtering field, that calculation will have to be done in a trigger so that it updates a non-formula field that can then be used as the filtering field.
That is a fairly simple trigger (compared to all the cases you have to handle to do the roll-up via triggers) so the combination of that trigger and the roll-up field is the approach I suggest.