Hi Manizheh and welcome to the website. Being so far from home must be lonely for you. Sometimes it's difficult to talk to others about our worries, especially when we have had breast cancer. Here, however, you will find many women who have had the same experience and who share your fears.
PJ is quite right about weight gain being a side effect for many women who take Tamoxifen. I think if you are worried you should try to have a check-up. Ask some people at the university about cancer doctors in Malaysia and make an appointment. The doctor should be able to help you be less worried.
Manizheh, you must be a very brave lady to have gone through breast cancer treatment and to be studying so far from home. You must use your courage to deal with your fears and worries. I make a picture in my mind of a big box and I mentally put my worries into it and put it away. I find it helps to do that as it stops me thinking about frightening things.
All of us who have had breast cancer are sisters in a very special way. There is PJ in America, me in Australia and you, an Iranian lady in Malaysia among all the others. We will think of you and pray that you find the courage to put away your fears.
Good luck with your studies, Sister. Sue