I had a similar situation, though I'm a bit older, and I asked why not do the needle biopsy right away? The doctor said there was no reason to unless the nodule (which is what I had, not a cyst) changed or grew. That seemed reasonable. Six months later it had grown, they did a needle biopsy, and the results were benign. Given that you have semi cystic breasts, the course your doctor is recommending seems reasonable. If what they saw on the sono was very concerning, they would probably want to do the biopsy right away.
It's hard to put it out of your head, but that's what I tried to do for the six months. I also monitored my breasts for changes (discharge, etc.) during those six months, knowing I could always go back if I saw a change.
Good luck,
A.