Armpit lump?

Hi,
I am a 19 year old male.  I recently discovered when i raise my right arm, there is a 'lump'.  However, i cannot tell whether it is normal as in a muscle or bone from my shoulder area or indeed a lump.  I can see it when i raise my arm straight up, and it is kinda in the area where the arm meets the center of the armpit.  It is rather large, around a golf ball size.  On my left arm there is a very similar 'lump' but just a slight bit smaller.  Is this just a normal muscle or something, or is that not a normal thing for the armpit. It started feeling tender, but I keep getting nervous and poking it so I think that may be what is causing that.  Sorry if this was a little confusing.  Also I think this may have been here for quite a while, I just am nervous and cant remember and am just trying to make sure it is alright.

Thanks for any help,
Matt

[Dnmh]

While there are lymph nodes under your arm, swelling of one or more can be caused by a number of things, not just cancers. Does the lump move? Does it feel hard or spongy? Can you feel it when your arm is down and relaxed? Do you have any other symptoms?
A little more info and I may be able to give you a better idea.