Hello,
Welcome to healthcare magic
You seem to be having a condition called as chronic
urticaria.
In majority of the cases, it is not possible to find out a cause for the urticaria, which is when we call it is “idiopathic”.
In few of the cases, it could be due to a specific food, medications and infections, or auto-immune.
As you have Hashimoto's chance of your urticaria being auto-immune is higher.
Some times treatment of
thyroid status cures urticaria, but urticaria should not decide the adjustment of
thyroxine. Your TSH levels and T3, T4 levels should decide your thyroxine dose. Your
endocrinologist will take a call on that.
Taking
cetrizine for long duration is not harmful. Continue taking antihistamine regularly in a minimum dose required to control wheals. It might stop one day, till then be comfortable.
Hope this helped
Take care