Small lump on my throat.?

i have a lump on my throat that comes and goes. the first time it came was about 2 months ago. but it went away after 2 weeks. it has been reappearing though. and now it is back. my doctor said it was a swollen lymphnode. the lump keeps appearing in the same spotunder my chin on the left side. and i wondered if it was a swollen lymphnode then why is it just one? wouldnt all of my lymphnodes be swollen? right now it is about one inch in diameter. should i be worried?