Hypothyroidism is a common post partum manifestation in many individuals. Hypothyroidism in itself can cause a myriad of menstrual abnormalities ranging from menorrhagia to oligomenorrhea. In your case however it could be leading to oligomenorrhea in its very early stages where your menses either don't bleed as they used to or have shortened in days of bleeding and in late stages can lead to a completely missed period. Scary i agree but absolutely treatable!
Firstly the dosing of thyroxine in hypothyroidism is a weight based formula where you calculate based on your body weight and then prescribe a slightly higher dose filling which the dosage is titrated to maintain a
TSH within normal limits. So I feel that your dosing of thyroxine is inadequate at present and needs to be changed to appropriate levels to prevent systemic manifestations.
Secondly, if you want to confirm this then you could run another TSH and a free-T4 level after 4 weeks of taking thyronorm 25 mcg to see if your TSH has been controlled or if it requires a higher dose to fix the issue.
Now when it comes to stopping the thyroxine tablet many considerations are to be made. If with the dose of thyroxine your TSH comes under control then the dose can be titrated and adjusted slowly but steadily to lower doses until there is a point where you would not require them at all. However, let me inform you that it is a time consuming process and sudden stoppage of thyroxine out of the frustration of popping pills everyday can lead to dire consequences.
Next Steps
I would suggest you change the dose of thyroxine to the appropriate dose then I feel you will find a general improvement in quality of life. if you want more suggestions or recommendations then feel free to contact me! I am always happy to help.