I have spent the past three months researching this same topic. I am someone who is also too low on red blood cells so that is part of the problem. But I have found after doing all the thyroid tests, that JustLookin mentioned, I added in the antibodies and found they were all negative, so I am definitely not a hypothyroid person, but I had already done lots of research and found out there is a condition called Euthyroid or Non-Thyroidal Illness Syndrome NTIS.
So the two tests that did show a problem were….a very low, below range T3 and also above mid-range reverse T3 which happened because I am always dieting and don't eat a lot, so apparently the body creates more reverse T3 to slow down the metabolism. That is not good because I now have no energy to do any exercise, so that sounds a bit like you wanting to stop and rest.
You can look up the terms. It is a situation that does exist and it does not mean the person has a thyroid issue that is long term. There is a short term solution and I will be doing it for the next 2-3 months.
A very fast test you can do yourself is find out how much your temperature is in the morning before you even get up to go to the toilet. Mine has been in the 95-96 F range and the average for the middle of the day for a normal healthy person is 98.6. It would be normal if I were 98.2 on awaking, as temp does go down while asleep, but when I am 95.2 F like I was Aug 19th I was so tired I could not do anything. It means my temp is 3 degrees lower than it should be.
The body builder sites say that each 1 degree below the norm means a 13% reduction in metabolism. So I am therefore 3 degrees below what it should be which means my metabolism is 39% worse than it would be if I had enough T3 action actually happening, but the reverse T3 was nature’s way of trying to slow down the body in face of starvation. So I suggest at a minimum you should do repeated morning temperature checking. You might not be as badly off as I have been. You might be only 1-2 degrees lower, but that still creates fatigue.
And if you do get the TSH, FT3, FT4, above all don't forget to get a “Reverse T3 test”...insist on it...because lots of doctors say that is a dubious theory, but there are several doctors who do understand it. Believe me I have read on the topic for three months now trying to solve a likely similar fatigue problem. In Canada they do not offer the Reverse T3 test and I had to pay to get it done, just $35 but I insisted because I was reading about it….and it turned out to be precisely what my problem is.
So, don't worry it doesn't necessarily mean you have a hypothyroid problem that is long term. You might have all the symptoms, but if it is because of the terrible reverse T3 issue then that can be solved fairly quickly, and you could be back to normal in 2-3 months.