Hrmsh, I am not a doctor, Not even a medical student. But in the last few month's I have learned alot dueue to endless searching on the internet caused by my Health Anxiety.
Anyways, it COULD be a lymph node. But according to the size you said, About the size of a pea this seems well within the "Normal" size of a Lymph node in the area.
Most normal lymph nodes are about 1cm in size (0.5 to 2.0cm) but that size varies depending on the location of the node, and what activity is going on. Infections, cancer and many other conditions can cause it to expand as the immune system reacts to the problem.
From what I have read on the net Painfull swelling of the Lymph Nodes usually is an indication of a nearby infection.
On that site you can find some info about the Lymph Nodes, I hope this is helpfull. Avoid searching the internet, for it can literally drive one insane, To the point of needing Therapy, Like me.
Wether it is Taboo or not, I strongly suggest you just visit the doctor, it is his job, and lumps such as these should allways be looked at, Especially for women, But do not scare yourself to much, it is probably nothing to serious.
As for the pain in your arm I am afraid that I have no idea what could be causing this, Maybe it is part of the infection, Maybe the bump might be pressing against a nerve, It could be alot.