I've been treated for breast cancer.
I've been treated for breast cancer which had spread to my back. I had chemotherapy followed by radiotherapy to both my breast and back.
I am so sorry that you have been so unwell and have had so many heavy duty treatments recently. Diarrhoea and sickness are unfortunately common side-effects of chemotherapy and radiotherapy. It is rather odd that you continue to suffer, but only once per week (I presume your bowel motions are normal the rest of the week). I don't have an explanation for it and medication would probably not help such intermittent symptoms. If the symptoms become more frequent you may need further tests and treatments. I really hope you stay well.