Large swollen mass in breast

My left breast has been a little tender today and on checking it now I can feel a large, kinda flat, bumpy mass. It’s very tender and sore to touch, and it can be moved around a little. It’s about an inch across.

I came on today so guessing it’s hormonal but I’ve never had anything like this. Also been feeling extremely tired and weak/shaky today but is unusual for my first day.

Thoughts?