Your TSH isn't all that low and if you don't have symptoms of being over medicated it's probably nothing to worry about.
My biggest question is whether TSH is the only thing they're testing or if they tested Free T4 and Free T3, as well, since those are the actual thyroid hormones. TSH is a pituitary hormone that doesn't necessarily correlate with actual thyroid hormones. It should never be used as the sole basis for diagnosing a thyroid condition or dosing medication.
If they tested Free T4 and Free T3, it would be helpful if you could post those results, along with their corresponding reference ranges.
How long have you been on the 75 mcg Levo and what, if any, symptoms do you have?