I may be able to offer some temporary info to help reduce your worry until you can get to a doctor... even if it does involve a bit of an embarassing story for me. One day I too noticed some seemingly huge bumps on the back of my tongue when I was obsessively checking for signs of HPV. They were so far back my tongue hurt the next day because I was sticking it out so far. I was convinced I had warts and scheduled an appointment with my doctor. During my subsequent internet searching, I happened across a site describing the anatomy of the tongue that mentioned 'circumvallate papillae'... essentially huge taste buds in a row at the very back of the tongue. Sure enough... the nurse doing my vitals basically took one look and laughed at me and confirmed that's all they were. Stupid HPV.
Here's the wiki site for it that gives a good overview: http://en.wikipedia.org/wiki/Circumvallate_papillae
A quick google image search will also give you some good pictures to compare.
Hope that's all it is!