What Causes Swelling/lump Under Chin?

i noticed a painful lump under my chin about 4 weeks ago i went to see my gp who told me that it was possibly a blocked salivary duct/gland and that it should go on its own.

whilst the lump has gone, there is still quite a large swelling under my chin. it is more noticeable when i lift my head back and swallow.it is not overly painful but is a little tender. although i am a smoker i am in general good health with no other problems. i do have a problem with one of my back teeth which does have to be removed, again i have no pain with that tooth at present but did have an abscess a few months ago which was when they told me the tooth had to go. could this be related to the swelling under my chin??? or what else could be causing this swelling?? any help would be much appreciated. thanks sarah