Can you fly domestic with a expired visa but valid passport?

No. You won't even be allowed on the departing plane without a valid Passport. A valid passport IS required to re-enter your country of origin. The country you went to should have not let you enter unless you had at least 7 or 8 months remaining before your passport expired. You might call up the US consulate and ask what procedures you must do to return to your country. Passport expiration dates are the responsibility of the passport holder.