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You are probably having secondary infertility
if you have not conceived in 8 years without using any contraceptive
methods so you need to get investigated for the cause of infertility.Before conception you need to to have proper control over your thyroid
as advised by the doctor but if you don't tolerate the medicine well please consult your treating doctor for dosage adjustment ;he will help but please don't take medicines in reduced dosage by yourself it will cause you more problems.