I had a lymph node under each armpit swell up after upping my Iodine. I got them to return to normal pretty quick by jumping on my rebounder, using castor oil packs, and taking Epsom Salt/H2O2/Baking Soda baths.
Not sure what could have caused your problem. Try puting a small castor oil pack on it. Also, try and get your lymph fluid moving.