i can't give you excellent advice on this, as my knowledge on the topic is rather rusty... but from what i do remember.
you have lymph vessells that run as veins through out your body carrying lymph flluid (i think that's the name of it (i know after you eat a fatty meal it gets milky and is called chyle)). and then you have lymph nodes scattered in groupings across your body. the lymph nodes are responsible for filtering out the lymph fluid and for generating white blood cells to some extent (though very little). that about all i can remember anatomy wise. you've heard of lymphoma, it's cancer in the lymph node (or is it vessels?).
but i also remember that it's a sign of infection. when you get a sore throat a doctor rubs your neck, he's not trying to get a you, he's checking for swollen lymph vessels. same as if you had a severe infection in your foot, the lymph flowing up would be carrying all kinda crap, and would be filtered by the lymph nodes in your groin.
as far as your armpit, i'm trying to remember what else that could be but i'm drawing a blank. it might be something else, or there might be another name for it when you have swollen glands in your armpit. sorry bro, i just can't remember.
like i said, you're probably fine. but if it persists, see a doc. also, monitor your temp. monitor the lump. any drastic changes get seen.
sorry i couldn't provide more info. i'm getting rusty.
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