Well for starters, as the saying goes, "A pint's a pound the world around" and you drank just over 3 pints of water just before your visit, so that's 3 pounds right there meaning you are 4 pounds heavier now than you were last summer. That much can be accounted for by water retention or TOM or heavier clothing due to the colder weather, etc... and may not indicate a problem at all.
As for thyroid, are you experiencing any other symptoms of low thyroid such as hair loss, unusual fatigue not relieved by adequate sleep, cold hands and/or feet, dry skin, dry brittle nails? If not, then the doctor may be wise in not rushing into ordering tests that you may not need and waiting to see what happens in the next few months.