I can't speak to the Erbitux because I didn't have it. You will definitely develop an altered/diminished sense of taste, and it won't be pleasant. I suspect the timing and severity of the taste distortion depends on the target of the radiation. In my case the nasopharynx was apparently the target, even though I'm an 'unknown primary'. Your tongue is recieving the radiation?
My taste went away fairly early in treatment, however, and has barely returned nearly 5 months afterward. The thick saliva is annoying, and there's not (as far as I know) much you can do about it. I found that if I took a glug of water and swished around my mouth, the thick stuff floats to the top where I can spit it out. That and lots of Kleenex.

Your radiation oncologist (RO) should be monitoring you closely. I'd discuss this with him.