If you are a freelancer, your income is often unstable. When I was starting there have been months when I didn’t earn anything, and when I did earn something, it was less than $5 a month. Now, that I have a lot of designs in my online stores, I get regular royalty payments each month, but the amounts vary wildly.
The best months are November and December when people buy gifts. Black Friday, too, has a massive impact on sales, of course. That makes up for the months when sales are lower. At the start of a new year people spent less, many probably need to rebuild their depleted savings after Christmas.
It might be scary for new designers when, in some months, they are only paid a fraction of their regular earnings. I remember it was for me. When I saw how my sales dropped in January and February I worried that it would continue. But sales always pick up in March, or April at the latest. After that, the income is fairly regular till October, when it picks up again for the next two months. And the cycle continues.