Trying to Create a Moving Average with irregular dates

So I have a dataset of CTD measurements that are roughly weekly from 2002 to the present. I've already formed these as averages from a larger dataset, and I'm trying to average data from every two weeks within for each month. My issues with this are that there are varying numbers of counts per month and large gaps, whilst also being such a large dataset that I can't do it by hand. Any help would be greatly appreciated.