make sure they also tested FT3 and FT4. If these are low, your baby may need thyroid replacement.
Worst case they should at least be retesting in a week or so to see what's happening.
Follow this up closely, proper levels of thyroid hormone are critical for your baby's normal developmeent.
I'm not sure what the recommended level for TSH is for infants; I believe it is higher than for teenagers or adults. There should be a reference range on the lab report, indicating what "normal" is.