After Three 2-week Tries, my Teeth Are Still Yellow

I had my teeth molded at the dentist and they sent me home with the Kor Night whitening syringe. I tried 2 weeks, but gave up at about day 10 when I saw no improvement and felt terrible tooth pain. I tried again, thinking I didn't give it long enough the first time. About 7 days in, more important health issues interrupted my teeth whitening journey. Then again...2 weeks in, tooth pain and hardly any improvement. My dentist never followed up or had in-house whitening treatments. They never brought it up in subsequent visits for cleaning, either. It was just forgotten. Am I missing something? Was the dentist supposed to do a treatment in-office? I've had no positive results.