Initial few periods after delivery might be irregular.
Second probability is that of pregnancy
if you had unprotected (not used contraception
Its very rare to have delayed periods due to TSH
value of 10.
Its better to do one home pregnancy test to decide the cause.
Also its better not to stop Thyroid
medicines without consulting doctor. Your second TSH value was normal because of medicines & not because of cure from thyroid problem. You should continue medicines.
Wish you good health.