Should I be alarmed about a thyroid nodule?

I'm a 20-year-old female. I went to the ENT yesterday for a sinus infection and he noticed a large lump on my thyroid. I noticed it a while ago, but I didn't know there was anything unusual about it. I don't have a thyroid condition, and no other doctor has ever noticed it before, but he scheduled me for a sonogram in 2 weeks. I used to smoke, and I have a family history of at least 4 different types of cancer (not thyroid cancer, though). I have a very sick feeling in my stomach. How concerned should I be?