I dont know if we anything in common, but I found your case interesting cause Thyroiditus has never been mentioned to me and I only saw an endo once right before he sent me to the surgeon. This was 2 and a half yrs. ago. I had cold nodules all over my left Lobe and a very large goiter right in the middle of my neck, couldn't swallow very well ,I lost alot of weight cause i wouldn't eat after choking on meat & breads a couple of times. They put me on Xanax for panick attacks it was scarring the hell out of me thought I was gonna choke to death. my blood levels were all normal. No Hypo or Hyper. Surgeonn removed left lobe & the goiter. Last weei had a new Ultrasound. It showed my left thyroid is 7.5x2.1x1.7 and is enlarged. On the medial side there is a mass measuring 2.2x1.9x1.7 and a cyst and a nodule and the enlogated part has calcification. My surgeon says it makes no sense cause he removed the left side. So he's sending me for a new ultrasound and a thyroid scan the nuclear one.I have to wait 3 weeks. this freaks me out a bit cause that sounds so big and it doesny make sense and its starting to hurt a little. This thyroid business really stinks. I'm sorry for your troubles. I hope all works out well for you.
Follicular cells are normal thyroid cells. The scan may be difficult to interpret with the recent contrasted-CT (iodine load)...but if clearly a hot nodule, less likely cancer. Calcification may mean long-standing nodule, but some calcification patterns are suspicious.
The growth may mean some bleeding into the nodule -- which does happen commonly. Without significant pain and lab abnormalities, this is not likely a (sub)acute thyroiditis. - it's certainly not an acute thyroiditis (that is a severe infection and not subtle).
A specialist is a good next step as removal may be the best option especially if there is anything suspicious on second opinion of the FNA biopsy (which the specialist will want) or if you have any compressive symptoms.
With all that is going on it sounds like you should be on thyroid meds after surgery, which sounds like where you are heading. (It really wasn't that bad.) Google side effects of Synthroid and also Armour in case you have to be on meds - this way you will be more informed about these two leading drugs.
How can it be benign but with follicular cells - aren't follicular cells cancer? I would look that up on the internet and do whatever I needed to do to get those things out of there! To me it is always better to be safe than sorry. I wish I had that option - but my papillary thyroid cancer had already invaded 2/3 of my lymph nodes by the time I knew it. Don't take a chance with your life! Do preventive steps if you can!