Armpit / health question?

Lately, when I've been showering, I've noticed that my right armpit seems a little "thicker" than the other. I don't feel lumps, just kind of "spongy tissue." It also itches, but probably from me poking and prodding it too much. Is this something to run to my doctor with or just let it ride? I don't want to be paranoid, but I don't want to be irresponsible either.