Fibroids

So on sunday we got told that I have a large fibroid at the top of my uterus and was given a week to see if this tumour would grow or not.

However, only 8 years ago I sadly had an accident and a benign tumour was found in my knee and it meant I became unwell, it drained me mentally and physically.

My midwife literally hopped out of her seat when i told her, as at my previous 8 scans nothing had been picked up only a Cyst on my ovary which went away on it's own. And rang the hospital I'm due to deliver at and said it was an urgent that I had another scan in depth and advised I packed my bag...

I'm now worried, is she doing it as a precaution as I've read on nhs it's common but only in the first trimester and I'm in my 3rd trimester now. Hopefully know more on sunday but my last tumour grew at quite some speed so I'm terrified. Any advise, someone had one before? What can I expect?

My bmi is 29 so classed as healthy, I'm white british, I'm only 21, and my bloods are all fine, no abnormalities...as these are what nhs website make someone a risk of fibroids.