Can you let me know how many times should I be tested for hypothyroidism?

Right testing needed. It is not the number of time your TSH should be checked but rather finding a doctor who will do the correct thyroid tests. Tsh is not enough to diagose problems. Also need thyroid antibodies, free t3, (liothyronine) reverse t3, (liothyronine) and free t4.
Every 6-12 months. And sooner if there has been a dose change. If it is a toddler or infant, then more frequent monitoring is needed.