thought I found a lump in my breast, just my period?

Ladies who has ever heard of this?! I was panicking thinking I found a lump in my breast and started doing some research about how to get screened for breast cancer and everything and found out that I should be doing a breast exam several days after my period and I was doing it the day it started, I am 25 and I never knew this and was wondering if other ladies had heard of this. The quote is from national cancer institute and the website is .gov so it's not like a Wikipedia source just who's heard of this and figured it was a good bit of info to share, I'd love to hear everyone's thoughts (ps I am still going to keep an eye on this and be extra sure to check for lumps and get screened and all that but for now I don't think it's anything to be alarmed about)