My daughter, aged 20, was prescribed an antibiotic for cold symptoms. She took them for about 5 days and it appeared she was improving, but now, she is sick again; sore throat, headache, sore body. She was tested for strep but it was negative, although that was the first day she had symptoms. She has had her tonsils removed. She is taking amoxicillin (sp?). Could she have developed an immunity to this antibiotic drug? She seems to get colds and the flu easily although she is otherwise healthy.