Lump on breast

Hi all, delighted to have found this forum. I found a large lump in my left breast a few weeks ago. My doc was very concerned and I had an urgent referral to Vincent’s. I had an appt with the consultant yest who said he thinks it’s a cyst but I still need to have a mammogram & ultrasound in a few weeks. The waiting now is killing me. Am I wrong to be worried as the consultant didn’t seem to be? Or should I just prepare myself in case it is serious. I am so tired with the last year, heavy legs full of fluid. Started HRT but it isn’t helping with the tiredness.