How does this lump feel when you touch it?

Most often, enlarged lymph nodes are found in the neck due to common infections such as a cold or flu.
A swollen lymph node in the armpit might be from an infected cut on the arm or finger, or from other type of inflammation.

the lump feels like a marble, and it's a little sore. It's about the size of a pea. I'm only 20, so I think that I'm going to wait and see if it get bigger or changes in any way before I head to the doctor. Also, it doesn't move around when I move the skin. Is it O.k. to wait, or should I be worried and go in. I've only been married 2 months, so I don't want have this turn into something more before I'm able to have kids. Anything would be great. Thank you

Have you noticed some pain or swelling in your arm, too?
Do you have some other new symptoms, general or considering your breasts?

Armpit lump that is almost painless, and not movable, can be suspected for swollen lymph node due to cancerous changes in breast tissue.
It's important to know that first cancerous changes due to breast cancer can be manifested as a swollen lymph node, even, if the breast seems normal on breast-self examination.