Just wanted to supplement the good info from Barb with the following.
I have no idea how hypothyroidism is typically tested and treated in your country; however, I expect that you probably face the same hurdles we have gone through at some time in our past. By that I mean doctors that have the "Immaculate TSH Belief' and only want to use TSH to diagnose and treat a hypothyroid patient. That absolutely does not work. Some doctors are willing to test beyond TSH, but then only test Free T4 and use "Reference Range Endocrinology", by which they will tell you that a test that falls anywhere within the range is adequate. That also is wrong. The ranges are far too broad due to the erroneous way they are established. Many of us say that symptom relief required Free T3 in the upper part of its range and Free T4 around the middle of its range.
A good thyroid doctor will treat a hypo patient clinically by testing and adjusting Free T3 and Free T4 as necessary to relieve symptoms, without being constrained by resultant TSH levels. You can get some good insight into clinical treatment from this letter written by a good thyroid doctor for patients that he sometimes consults with after initial tests and evaluation. The letter is then sent to the participating doctor of the patient to help guide treatment. In the letter, please note the statement, "the ultimate
criterion for dose adjustment must always be the clinical response of the patient."
http://hormonerestoration.com/files/ThyroidPMD.pdf
So I urge you to make sure that you are tested for Free T3 and Free T4 each time you go in for tests. Free T3 is the most important because it largely regulates metabolism and many other body functions. Scientific studies have shown that Free T3 correlated best with hypo symptoms, while Free T4 and TSH did not correlate at all. I also suggest that you should have a conversation with your doctor about all this and the letter above and find out if the doctor is going to be willing to treat you clinically, as described in the letter. If not then you should try to find a good thyroid doctor that will do so.
Also, since hypothyroid patients are frequently too low in the ranges for other important areas such as Vitamin D, B12 and ferritin, it would be a good idea to test for those as well. Whenever you have test results available please post results and their reference ranges shown on the lab report and members will be glad to help interpret and advise further.
Your symptoms are definitely those of hypothyroidism and your antibody tests would be basis for a diagnosis of Hashimoto's Thyroiditis. With Hashimoto's, the body thinks the thyroid is foreign and produces antibodies to destroy it. The destruction, typically, takes quite a few years, but as it happens, your thyroid will continue to produce less and less hormones, as healthy tissue is destroyed.
Yes, you're going to need to take thyroid replacement hormones, such as the Euthyrox, because you thyroid will soon, not be able to produce the hormones you need.
25 mcg is usually a good starting dose. It takes 4-6 weeks for the medication to reach full potential in your blood, so it's not likely that's the cause of your headache. If Euthyrox is a brand name, you shouldn't have any worry about it being fake. Some people do react adversely to fillers/binders that are used to keep the pills together. You might talk to your doctor about trying another brand, since different manufacturers use different fillers and binders. You might do well, with another manufacturer.
You might also ask your doctor about splitting the pills in half and only starting no half until your body gets used to having the hormones again.