What could be the reason for a huge fluxuation in Thyroid?

I had a blood test done about 2 months ago for a cholesterol research study and they told me my TSH level was 5.48. Unfortunately the cut off was 4.3 so I wasn't able to partake. I took another blood test about a week ago and my TSH level was 1.2 almost perfect and my Free T4 was fine also. Now 5.48 to 1.2 is a rather large fluctuation. I have many of the symptoms of hypothyroidism and my doctor is just blowing me off saying there is nothing wrong. Does anyone have any information that could help me out.