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You can wait for 7-10 days late for periods to come as periods can delay even with stress. Firstly get your thyroid hormone levels checked. If it is normal or you have hyperthyroidism
also you can have irregular period or missed period like this. But since you are taking Thyroxine you should rule our Prolactin
hormone elevation and Polycystic ovarian disease
by thorough checkup by Gynaecologist if your periods do not come. If Pregnancy test is negative, no need to take Folic acid
but if you are planning for pregnancy you need to have regular periods first which ca be done by contraceptive
pills provided by Gynaecologist advice only. Get thorough checkup by Gynaecologist to rule out any hormonal or ovarian problem.