I really do not understand why doctors are so poorly trained in treating patients with hypothyroidism. It is a very common condition but I suspect a lot of patients still have clinical symptoms.
I shall give you two links, and the second recommends T3 for fibromyalgia. You may not be converting sufficient T3 from your T4 (levothyroxine). Plus when we are underdosed with thyroid hormones, weight can be gained and many find it difficult to lose as their metabolism is so low to allow it. Even taking orlistat doesn't seem to be working and a rise in medication might do the trick or the addition of T3. I am not medically qualified but assume as your metabolism is so low and it is hypothyroidism which is the root cause that diet pills appear not be the answer.
You also have to request some of the blood tests recommended previously. You may not be able to afford private if you don't work. So ask your doctor if he would do them as you've been advised by the NHS Choices for advice on dysfunctions of the thyroid gland. They recommend the following tests to get to the root of why you aren't improving on levothyroxine.
TSH, T4, T3, Free T4 and Free T3, B12, Vit D, iron, ferritin and folate.
Many doctors do give 'extra' prescriptions for disabling symptoms when what we need is a proper dose, i.e. one that relieves all symptoms.
The new test should be the earliest possible, fasting, (you can drink water) and allow 24 hours approx between your last dose of levo and the test. Get a print-out with the ranges and post for comments.