I'm Taking Flagyl For Cdiff, This Is My Second Prescription,

I'm taking flagyl for Cdiff, this is my second prescription, I also came down with a cold while taking the medication. I have been taking the second prescription for 4 days now, my stomach is very upset and I don't feel well. My tongue is yucky, feels like is is furry, and nothing tastes good. I asked the doctor for a different prescription but he wanted to try this again first, said the other perscriptions are very expensive and most insurance companies won't cover them. I really just want rid of this, if it didn't work the first time why would it work the second time?
Is there something I can do to get rid of this on my tongue or do I have to wait til I'm done with my prescription?