Lump on Gum

I had a root canal done several years ago.  About 2 months ago, I noticed a lump on my gum right underneath the crown and the tooth became VERY sensitive, so I went to my Dentist, who gave me antibiotics and then sent me to an Endodontist to do another root canal through my crown.  They took several xrays which showed a large black spot on my gum.  After the proceedure, they gave me more antibiotics and told me to take them for four times a day for 10 days.  I followed the directions to the letter.  Although the sensitivity in the tooth stopped, the lump and pain in my gum never went away.  I contacted the Endodontist again and they had me come back in to take out the "filling", re-treat the root canal and put medicine in the form of powder inside as well as ANOTHER antibiotic.  This was on Tuesday and today is Friday, the lump is still there, it still hurts and I don't feel any closer to resolving this.  They said that they wanted to see me again in a few weeks to see how things are going.  
My question is this....have I taken way too many antibiotics and they are just not working anymore or might have they diagnosed the situation on the wrong tooth?  I am desperate for answers!

[scottma]

Seeing a periodontist is advised.