What Causes Delayed Periods After Stopping Thyronorm?

My Age is 24, Height 5ft 4inches. Weight- 58 kgs. I had my period first at the age of 13 yrs. My period normally occurs in a 40 days cycle at an average. It is normal for me. I had thyroid when last tested around TSH: 3.6. I take Thyronorm 25mcg daily. Last two cycles i have noticed a delay in my period. It is taking around 60 days.

Here i want to mention i stopped taking thyronorm for 1.5 months after that this problem occured and i again started taking thyronorm regularly from mid of May. I had my period upto April normally. then it happened on 1st wk of June and Now this month 1st of August.

Can u suggest that what could be the problem and a solution for having a regular period.

Need help