It sounds like you are being treated with some hotch-potch homebrew approach to treating.
There are two usual approaches to controlling hyperthyroidism - typically Graves.
First, take an anti-thyroid medicine such as carbimazole only. As thyroid hormone levels drop, reduce the dose. Try to keep the thyroid hormone levels at a good level.
Second, take an anti-thyroid medicine such as carbimazole in sufficient dose to fully suppress your thyroid making any thyroid hormone. Add in levothyroxine to supply all your thyroid hormone requirement. This is known as block and replace.
What you have described sounds like half way between the two. Trying to manage someone by adjusting both carbimazole (to allow some thyroid function) and also supply levothyroxine is quite likely an impossible job. Rather like driving by using both accelerator and brakes all the time.
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