The short answer to your question is that your struggles are proof of the opposite, that you are indeed a child of God. A truly lost person has no desire to know the Lord and would have no concern for the state of his own soul. Such a person would not “struggle” over assurance of salvation precisely because it would not matter to them. The fact that it matters so much to you means that in your heart you really care about the answer. That can only come from the life of God in your soul.
And as for “struggling” over assurance, I think the problem comes from looking in the wrong place. As long as you look at yourself, you will never measure up. Your love for God will seem deficient, your obedience halfhearted, your devotion ragged, your growth in grace dismayingly slow, and your propensity to sin far too great. As long as you look at yourself, you will find many reasons to doubt your own salvation.
Hebrews 3:1 gives us the answer: “Fix your thoughts on Jesus.” We are to look at him and rest our hope upon him. He alone can save us.
There is another way to say it. God is satisfied with the work of his Son. Are you?
That puts it in the right perspective. If God is pleased with what his Son has accomplished, we should ask if we are also pleased. If Jesus has done enough to accomplish salvation for us, are we satisfied with him? We must not look at the cross and think, “Jesus did his part. Now I must do mine,” as if someday when we get to heaven, we will put our arm around Jesus’ shoulder and say, “You and me, Jesus. We did it together, didn’t we? You died on the cross, and I mowed the grass at church.” It doesn’t work that way.
Either Jesus pays it all or there is no payment made for our sin.
I urge you to look to Christ and not to yourself. He alone can save you. There will be times when you feel closer to the Lord and times when you may feel far away. There will be times when your faith will be strong, and times when it will be weak. But those things reflect the vagaries of the human condition.
Do not look to yourself. Look to Christ and all will be well.