Tamoxifen and Vulval cysts??

Help! I’m 3 weeks out of radiotherapy and 3 months into Tamoxifen. Was just starting to feel a bit more human but have now developed a painful cyst on my vulva about the size of a 5p piece. Was hoping it would just go away but a week on and it’s showing no signs of improvement. Bathing, wearing loose fitting clothes etc and it’s not helping. Bracing myself to call th doctors, I’d got used to getting my boobs out but… ? I know vulval itching is a recognised side effect of Tamoxifen. Has anyone else had a similar experience?