Postpartum breast cysts

I just had a baby 10 months ago. At around 3 months postpartum, I went to the gynecologist due to hardness in my breast turns out I developed many tiny cysts. I had never had cysts prior to my pregnancy. I had the check up down 6 months later to check on my breast again. This time I had several more tiny cysts and one which they are unsure if it’s a mass or not. Are cysts and masses a common thing after pregnancy? I’m worried it may be something serious.