Is this caused by Tamoxifen

Hi any similar situations would be great to hear about,

January 2019 grade 3 triple positive breast cancer diagnosis in left breast (aged 34) left breast mastectomy was chosen route, followed by 4 EC stopped after 3 due to sepsis, then 12 paclitaxel stopped at 8, I was then put on herceptin 9 of 18 completed due to Covid 19, in December 2019 reconstructive surgery was completed I then began Tamoxifen late February as was really nervous to begin 2 weeks ago I started to feel an uncomfortable feeling in my armpits (both) this has now spread to sharp pains in my breasts (both) pains down my arms neck and back I have no visible lumps or swelling, I spoke to the breast care team who said it’s probably hormonal and left it at that my gp has offered to check next week as it is really painful.

i am trying not to be alarmed therefore wondered could this or has anyone experienced similar symptoms on Tamoxifen.

many thanks in advance