If this is related to secondary breast cancer, your team would be the right people to advise you and to recommend what would suit you best. In some cases, it might mean physio, or maybe a referral to someone to look at your posture. You may possibly be physically tense from anxiety.
Your team should also be able to help you with a referral to occupational therapy. As someone with breast cancer, you are registered disabled. You may well need a proper assessment by your employers/Human Resources of your work station, your actual chair, all the ergonomics of office work that get overlooked till the back pain is there! Your employer should then provide you with any recommended equipment such as foot rest, adapted chair, back support, a standing-seat, whatever is necessary for your wellbeing. You certainly shouldn’t have to tolerate back pain when working in an office, regardless of breast cancer!
(I only know this because I had to do a presentation about healthy work stations once!). I’d also advise you to check your rights under the Equalities Act (which replaced the Disability Discrimination Act). You may not feel disabled but, by law, you are. The knowledge may prove useful.
I'm facing back pain issue from last 3 months. I'm also taking pain killer medicines, but still facing same issue. I have office job from 10- to 12 hours. I have long hours office job. I'm facing back pain issue due to my long hours office timing and by sitting long hours at one place. Please suggest me best solution forback pain .