Can my husband take me back after my waiting period from a single divorce has ended?

A revocable divorcee becomes irrevocably divorced upon the expiration of her waiting period (iddah). So, if your husband divorced you with a revocable divorce and three menstrual cycles have passed without him revoking the divorce, then you are irrevocably divorced from him. He is not permitted to take you back except with a new contract, fulfilling its pillars, which include the presence of your guardian (wali) or his representative, along with two just witnesses, and a formula indicating the contract.