Survivor since 2012
I don't think "worry" is the word you should think of right now. Think ACTION. It's most important to get yourself to a doctor you trust, who will probably want a mammogram, ultrasound, MRI, or some combination of all three. They can tell a lot by those tests about what the "gland" might be.
Take this step by step and try very hard not to get ahead of yourself. This could easily be nothing other than a swollen gland. But you need to get to the bottom of it as soon as you can. Best of luck to you.