Lump in armpit, and I’m terrified

So this morning as I was in the shower I noticed my armpit was tender, as I felt around more, I noticed there was a lump that was the cause of the pain. It’s about the size of a golf ball. I am making a doctors appointment ASAP, but this has me shaking 😭 I’m 28 ,a mom of two, and healthy, I don’t feel like this could be a cyst/boil . I feel so scared.

It’s hard o see the lump in the picture, but i can definitely feel it.