It's best to wait and see what your thyroid level comes in at and ask your Doctor if it's underactive or hyperactive.
I've had an underactive thyroid gland for years and i'm taking thyroxine for it but some people do add weight gain but whatever the outcome your Doctor will try your on a certain dosage and usually thyroxine is the drug they put you on and take regular bloods to see if it's balanced in your system correctley to help your gland.
I'm very thin and my gland as it's days of going hypo so i loose more weight...it's just getting the balance right to help you.
I would'nt get worried about it and please keep we updated on your results
Raynauds phenomenon, Psoriasis, scleroderma, Sjogrens Disease, Antiphospholipid Syndrome, Megaloblastic anaemia, DLE, SLE, Hypothyroidism etc