breast cyst

Heyy :)

I have a, what I believe, is a cyst on the left side of my breast And I don't remember the last time I had one so I'm kinda worried if it's a lump? It's about 3 fingers away from my nipple and hurts when I pinch it. My period is coming up soon and my diet has changed majorly (eating a lot more chicken and dark green vegetables and stopped drinking caffeine) is this a period symptom?