My husband didn't have chemo but had a ND and radiation. He developed the pain upon tasting food after the ND. He described the pain exactly how you are describing it. He said it just happened with the first bite and after the pain stopped he could go on and eat the rest of his food and be fine. The ENT told him it was due to nerve disturbance and would clear up. It lasted a while but eventually it did go away and he is fine now.