Of the multitudes of questions which can be asked of someone about his/her spiritual life, my favorite is: "Has the Lord Jesus changed you?" For when a person is genuinely regenerated by the blessed Holy Spirit, there is a radical change, and the person knows it. I know my theological stance on salvation is punctilliar, meaning a certain point in time. No doubt some embrace the possibility of a gradual change by the Lord, but I am not one of them. As varied and creative as the Holy Spirit's means and methods are, I do not see Him gradually regenerating anyone. There is a moment, an instant, when He vivifies the spiritually-dead person's spirit, transferring him/her from the kingdom of darkness to the kingdom of light. Now, to be sure, depending on the individual's age, competency, awareness, etc. the realizing that this change has taken place may be in stages. Yet, I would insist, from the blessed Holy Spirit's perspective the change is instantaneous.
If one has no recollection of a time when he/she was not a Christian, some serious reflection on the Scriptural doctrine of salvation would be in order, as well as seeking the Lord for either assurance or conviction.
There are few greater joys in this life than to know that you know you are saved and on the way to an eternity with the One Who saved you.