@kristenr0306, if you're talking about the 50 free listings that come with a basic eBay account, yes, they are allocated on the first of every month.
You should be able to find any/all "promos" related to free listings if you go to My eBay > Selling (scroll down to the bottom of the page).
If you're using the Seller Hub, go to: Seller Hub > Overview (scroll down the page and look for the section titled "eBay Promotional Offers").
If you can't find the promo you thought you activated for 100 free additional listings, then a) You may have not activated it even though you thought you did; b) The offer may have expired as many times those types of promos are time-limited, meaning you have to list/use the promo offer by such-and-such a date. If you don't, the offer disappears.
Promo offers for something like 100 additional free listings are randomly distributed and it is not unusual not to receive one for months. If you find you are consistently using up your basic free 50 listings every month, you might want to consider a "Starter Store" which will give you 100 free listings every month for a subscription fee of anywhere from $4.95 - $7.95/month depending on whether you select an annual subscription plan or just go month-to-month. More info can be found here: https://pages.ebay.com/seller-center/seller-updates/2018-spring/ebay-stores.html
Hope this helps.
