How can I tell difference from my mammary glands or a lump?

I self examined my boobs just a few minutes ago. I felt these little bumps on my left boob. Which I’m pretty sure it’s just my mammary glands but the thing that is I guess making me uneasy is the little bumps hurt more when I press on them and are a lot more prominent on my left one than my right one. I’m 21 years old and a cop so we have to wear these pretty heavy vests for over 12 hours almost every day. I usually wear padded sports bras at work to protect my boobs from being completely smashed by the plates. I want to say about a week ago maybe a little longer I wore a bra without the padding and my left boob was hurting all day and still hurts to this day. Which is why I decided to examine myself. It’s very tender, i feel it more on the top left side. Also it’s not the first time, every now and then my left boob Is tender in the same way in the same area, which is another thing that makes me uneasy