Did under eating cause my elevated TSH levels?

Elafacwen

Background: 5'8" female, 217lbs. I am down 41lbs since November, and I have lost 31lbs in the past 90 days. Grand total is 48lbs lost since my heaviest last April.

I recently has blood-work done and my TSH levels came back at 18.6. I had free T4 tested as well, which came back as .83. I had total cell count and some sort of kidney test done as well, however, I will not have access to the rest of the results until I get them them in the mail. The nurse I spoke to over the phone did not mention if those results were abnormal. I have an ultrasound on my thyroid on Friday because it is enlarged.

I will admit that I have been under eating most days of the week. Some days I will only consume 800 calories because I am simply not hungry, and I usually stay below 1200 and above 800, except for Friday, Saturday, and sometimes Sunday, where I hit around 1500-2000+. I have been under eating during the week for about 2-3 months now.

They currently have me on 50mcg of Levothyroxin until June where they will re-run the blood work. I had many symptoms pointing towards hypo, some of which started in high school but regressed a couple of years ago, only to blow back up in the past 6 months, around the time I started losing weight.

Now the big questions: Did under eating cause the increase in TSH levels? I plan to speak to my doctor on Friday after the ultrasound.