"Very disappointed"

Gave a urine sample in to surgery on Friday to be told that day that no significant infection but would send for further investigations. Today Wednesday - 6 days later - I receive a message "confirming an infection and prescription send to my pharmacy." How can the same sample produce a different result 6 days later and what if the infection had caused me to be admitted to hospital? How can this happen? Earlier last month I asked if my Polymyalgia had returned as I was getting unilateral pains in my arms,neck etc. to be told there were no appointments and to go to pharmacy, download the LIVI, visit the Woking walk in centre, St. Peters A&E triarge or try again for another appointment!