Actually, pilonidal cysts never go away on their own. The infection that, at times, occurs can clear but the cyst stays...unless surgically removed.
That doesn't mean every pilonidal cyst needs to be removed. If there are frequently recurrent infections/ abscesses, then the cyst should be removed.
If it seldom becomes infected, then it doesn't hurt to leave the cyst. As are so many things, it's a judgment call if and when to remove.
While it's not possible to diagnose you over the internet, this sounds a lot like a pilonidal cyst. It isn't likely to cause any long-term problems, and sometimes they go away on their own. However, you should see a doctor, because if the cyst becomes infected, you'll need treatment. Here's more about this type of cyst: https://www.mayoclinic.org/diseases-conditions/pilonidal-cyst/symptoms-causes/syc-20376329?page=0&citems=10
My son had one, and it kept coming back. It was surgically removed about 8 years ago, and he hasn't had a single problem since then.