JosephineB1 ... everyone reacts differently to different drugs - so your Onc really should have been listening & believing your side effects and acted appropriately, trying a different one that 'may' suit you.
I only lasted 6 weeks on Letrozole as my side effects were really nasty .... but my original Onc didn't believe me. I saw his Locum next time (he was on leave) & told her the same - and she believed me & after a break (for a number of weeks) she swapped me to Exemestane. I then also swapped over from my original male Onc, to her!
It took 6 months for Exemestane to reach the same level of discomfort & pain as the Letrozole ... and I was then swapped over to Anastrazole (after a few weeks break) and was on it for the next 7 years.
I actually just finished my BC journey with my Onc today!! YAY!
You are allowed to swap Oncologists if you think you are not getting the service you require ... just as I did. A 2nd opinion is also invaluable.
take care & all the best