Weight gain is the commonest question on the forum. It is puzzling to the people as they've not changed their way of eating.
Many women become hypothyroid after delivery and I'm sorry you are hypothyroid.
First, hypothyroidism is a serious illness if untreated and levothyroxine is the only prescribed medication in the UK. So we have to take it faithfully every single day - on an empty stomach with one full glass of water and wait an hour before eating. Most usually find taking it when we get up the most convenient.
Weight gain is a clinical symptom of hypothyroidism and it is because our metabolism is so slow due to few thyroid hormones. Exercising also isn't a good idea as it depletes the most important hormone, T3. Levothyroxine is T4 and it has to convert to the Active Hormone T3 and it is T3 which is required in our receptor cells. Exercising before being on an optimum will deplete T3. We can walk or swim but not excessive.
It has probably taken years for us to become hypothyroid, slowly, slowly until we go to GP. So it takes a while for levothyroxine to be slowly increased until our TSH is 1 or lower with a Free T4 and Free T3 towards the upper part of the range. These two are rarely tested.
There should be no side effects to leovthyroxine - only the clinical symptoms of hypothyroidism which, when you reach an optimum of levo your symptoms should resolve.
Due to you having Hashimoto's - an Autoimmune Thyroid Disease - and it is the commonest form hypothyroid as it is the Antibodies which attack your thyroid gland until you are hypothyroid. The antibodies wax and wane and sometimes you will feel hyper and at other times hypo.
There is no quick fix. To help reduce antibodies gluten-free is very helpful.
We have to read, learn and ask questions if you want to get back to good health. The aim is to get your levothyroxine dose to optimum and it cannot be done quickly. A blood test every six weeks with an increase of 25mcg until you are symptom-free and feel well.
Whether you take or don't take levothyroxine, weight gain is a clinical symptom of hypothyroidism.
When you reach an optimum dose of levothyroxine your weight should reduce. The aim is a TSH of 1 or lower.
When you give results of blood tests you have to put the ranges as well. These are figures in brackets. Ranges are important for responses as labs differ and it makes it easier to comment.