i had a similar experience. it was right under my arm. i went to see my ob doc because i had to get an ultrasound and he said it was normal when your body is fighting off an infection. he said if the lymph nodes swell up usually at that time or within a couple of days you have a cold or infection your body is fighting off. once it subsides it's gone. that was a relief as i thought the worse as well!

hope doc gets some answers for you and take care!
hugs from buggy]]