Negative pregnancy result- missed period

My girlfriend usually has a regular period and it was supposed to be on this month 21 We had sexual intercourse 2nd of this month ie September and she missed her periods on 21st and we went for a urine test (home) on 23rd and 26th. Both turned out negative and no significant symptoms of pregnancy. She feels little bit cramping but it resolves when she uses toilet and now its been 7 days since she missed her periods. She has travelled a 5 hour fligh journey and had a fever upon reaching the destination. She was taken to hospital and had few IV s and antibiotics. So can i trust the results as the kit has a leaflet stated test can be taken any time after missed periods (we used early morning urine). Can you please share your feedback doctors