Sac in throat

I recently suffered a serious sore throat (headache, chills, no stuffiness) one the right side that I figured was strep.  It last the weekend, then broke and eased.  However, as I recovered, left side of throat became scratchy, raw, with white, pimply bumps (tonsils are out), and the left side of the peritonsillar arch (back of mouth, in front of where tonsils were) swelled up but did not hurt.  Finally went to the doctor, who said yeah, it was probably strep and prescribed strong Augmentin for 10 days (my first antibiotics in ten years, btw.)  Scratchiness and slight headache went away, but glands remained swollen and a balloon-looking sac has appeared in the back of my mouth and the base of the peritonsillar arch.  It's pink in color, painless, and it moves around when my tongue hits it.  I finished antibiotics this weekend and fever and headache have returned.  I am going back to the doctor this week, but I have no idea what this might be.  An abscess?  A regrowing tonsil?  Something more sinister?  I'm not too worried because it is recent and seems to be tied to this latest illness.  But I cannot find anything like it online.

[redontop4]

Sorry/  I should also add that I have had occasional earache, but doctor said my ears are totally clear.  Lymph nodes on both sides are swollen but not really sore.