Enlarged mottled thyroid on ultrasounds scan

[Alpops]

Hi.
Can anyone help? 6 years ago I had a biopsy, and ultrasound and an MRI scan following finding a lump at the front of my neck in my thyroid. All scans showed nothing and the biopsy was clear. I was discharged following a second opinion consultation. I went to the GP with a small lump at the top of my throat. I was sent for an ultrasound today the doctor wasn't really concerned by the very small lump saying it was a lymph node but said my thyroid was quite enlarged and mottled in appearance. The lump doesn't feel bigger than it did 6years ago. Wen I had the original tests my blood results were normal. Anyone any idea why I have enlarged and 'mottled' thyroid??? They said they will repeat bloods and maybe do another biopsy.
Any help would be grateful.
Thanks
Alice