I have been taking synthroid for at least 10 years, now want to get pregnant?

I’m a 31 year old female who has been taking synthroid for at least 10 years and who also wishes to get pregnant in the coming months. I stopped birth control in December. Had a normal period in January and February. In February my synthroid dose was changed from 50 mcg to 25 mcg grams because it tested below normal range. I have not had a period in over 60 days. Could my synthroid change have stopped my periods? Will going back on the old dosage bring them back? Time is of the essence in this matter. Recent lab works shows my TSH levels back within normal range.