More reasons no-one wants this disease. I was 43 when I started on Tamoxifen. After the first month or so, I didn't notice I was taking it. No weight gain. My periods resumed after about 6 months. The oncologist I was seeing just shrugged, I would be surprised, 10 years later, if they would be as sanguine as they were then. I took it for the recommended 5 years.
After my recurrence last year I decided, at 53, to get rid of my ovaries as I still wasn't menopausal. Now on Femara, it's too soon to tell how that will go.
Tanya, 18kgs more me would trigger the same response as you are having. No! No, no, no, no, no! Like everything else BC the links between cause and effect are difficult to determine because there are so many variables and such different responses from person to person.
If you are seriously thinking of ditching the drug, it's important to understand the ramifications and have other options explained. You may have to have a bit of a shop around and ask a couple of different doctors. They generally don't like taking risks so will usually not support you deviating from best practice.
Maybe ask what the feeling is about you taking a three month hiatus from it and see if that makes a difference to your weight gain. If it does, you may be able to say the drug is the culprit, if it doesn't logically there must be another cause. They may advise you the risk isn't worth it--which would be a totally reasonable stance. I guess you are the only one who knows where the line in the sand is for you. What ever you decide, please get the best advice you can first. Good luck