Unless you have palpable and /or visible swelling on the neck, the ultrasound is not the second step in your case.
Low TSH with normal T4 is usually indicates subclinical hyperthyroidism.
The next step can be the RAI scan --- low uptake indicates thyroiditis
High uptake indicates possible Grave's disease
High uptake in one spot indicates hot nodule [adenoma], which can be found by neck inspection.
Additional bllod tests can be recommended
ESR rate [to diagnose subacute thyroiditis which can be complication after respiratory infection]
Each lab/doctor has their own idea of what a "panel" consists of. It's an imprecise term that usually results in inadequate testing. Insist on that free T3 test.
To answer a couple of your original questions:
Having a cold doesn't affect TSH.
TSH has nothing directly to do with nodules. Many people who have totally normal TSH and no thyroid disease have thyroid nodules which never cause them an iota of trouble.
As I mentioned in another of your threads, low TSH combined with normal thyroid hormone levels (T4 and T3) can indicate a pituitary gland problem. But don't get too far ahead of yourself; wait and see what the thyroid tests show first.