Hopefully you will have an immediate ultrasound breast scan, they should be able to tell you what it is straightaway if they have the up to date equipment.
A word of comfort, benign breast cysts are very, very common particularly in peri menopause - apparently they come and go all the time and some women have loads of them. I had one once and I was worried but the breast specialist told me that never, in his entire career, had he seen a breast cyst turn into a malignancy - if it turns into a malignancy, then it was never a breast cyst to begin with. Also, having breast cysts does not mean you are more likely to develop breast cancer.
Hope it all goes well, please keep in touch.