Thyroid hormone replacement must be done accurately. You must get your
TSH checked every 3 months at an NABL accredited laboratory. The blood sample must be given after 12 hours fasting. Then depending upon that the correct replacement must be prescribed.
As for your question, yes, 62.5 mcg is a more sensible dosage instead of alternating 50 & 75 mcg.
Such alternating is only done when dose is being changed. You alternate between old and new dose till old dose medicine is over. This helps better transition to the new dosage.