Should I be worried?

I'm only 31, and am in great shape.  I run marathons, eat well, don't drink and don't smoke.  My grandmother died the week she was diagnosed with leukemia, and my mother had bladder cancer three times. About three months ago, I found a lump in my armpit at the base of my breast.  I didn't think much of it, but had my husband double check.  We figured it was an enlarged lymph node, and wrote it off since I'd been up and down with colds and the flu for about a year. Since then, the lump has increased in size.  My arm is going numb and I'm always tired.  (though that didn't seem alarming, since I'm a Marine and am currently in the midst of a really strenuous 6 month training evolution. The area is tender and sore, and I feel as though there's always pressure in that area, since the lump has more than doubled in size. Yesterday I ran a marathon and signed up for the leukemia and lymphoma team in training for future marathons... which was the first I'd heard of lymphoma.  For some reason I felt compelled to learn about the symptoms. I really don't want to worry.  I'm healthy.  I exercise.  I'm a Marine... which often makes me feel invincible.  But I did spend a year working in a building with exposed asbestos at my last duty station... which is when I started catching every cold and flu that came around. I'm asking because what I'm doing right now makes it extremely difficult for me to get an appointment.  I hope I'm being irrational, and that I'm connecting the dots in some sort of "House" and "Grey's Anatomy" fictional fantasy. Thanks for the time.