Swollen Lymph Node and Hair Loss

[cleverusername]

I am 23 and female.  Periodically -- about once ever 4-8 weeks -- on of my lymph nodes on my groin will swell up to about 3 cm in diameter.  For about three days, it'll be red, swollen and tender to the touch, and then disappear like nothing ever happened.  This has been going on for a little over a year.  Now I have noticed that I have a bald spot in my pubic hair where this lump occurs.

Initially I of course brought this to the attention of my gyno.  He monitored the lump by measuring it every few weeks for about 2 months.  He thought it was a benign tumor, and scheduled a surgical biopsy.  However, when I went in for pre-op, he noticed that the lump had shrunk.  He said that tumors don't behave that way, and dismissed the lump as my body fighting an infection.  He said, "you probably have athlete's foot and don't even know it, and should be proud of your immune system for doing such a good job!"  Give me a break.

I feared an STD despite my responsible lifestyle, but, after waiting an appropriate number of months after my last sexual partner, tested negative for everything I could get tested for: HIV, chlamydia, herpes 1 and 2, hep B, hep C, gonorrhea and syphilis.  

I should also mention that several months ago I took a course of antibiotics for an upper-respiratory infection, which has had no effect on my lymph node, and so I doubt the problem is bacterial.

About 9 months ago my dentist found a tumor in my gums, compounding my fears, which turned out to be benign (he suspects it was caused by irritation from the braces I had growing up).  I did find another lump on my gum, though.

So any clue as to what's going on?  Do I have cancer?  An autoimmune disease?  Some kind of viral infection?  What kind of doctor should I be seeking out? Gyno? Dermatologist?  Internist?  Someone else?

Any and all information or advice is greatly appreciated.  The hair loss is really starting to freak me out.  Could the hair loss be caused by irritation/pressure from the intermittent swelling?  AAHH!!!