Missed 3 days of 75mg thyroid tablets will it affect me?

It would effect but: It would effect but not as much if you start taking the pill and get your TSH checked and see if it is in therapeutic level. You have to understand, 75 mcg thyroid hormone is needed by your body daily to function properly. I mean daily. Your thyroid does not make enough hormone. If you miss dosage or TSH is not in range then you have to adjust dosage. Otherwise the symptoms would come back.

Not right away: First off you are probably taking75 mictograms. If you miss your medication regularly you will have hypothyroid symptoms which can include weight gain, cold intolerance, constipation, dry skin and mental slowing. So missing 3 days is not life threatening but not something you want to do.

No: The answer is that your thyroid hormone will be working for a while. Don't try to catch up on your dose as you can take the risk of side effect and worst would be the heart. Just go back to your prescribed dose and take it everyday.