Palermo,
Your experience of 'what ifs' - doubts, are what I was plagued with as well when I became a new Christian. But you are not going to give into doubts because you are now in Christ.
Yes it is Satan trying to tempt you to believe you are not really born again.
Remember when Jesus was baptized, straight away the Satan tried to tempt him by trying to turn him from God's will. How did he defeat him? By keeping to God's Word. You know God's Word is true and it can defeat any lie from Satan.
Do you have a bible? Start reading it, this will renew your mind and defeat any doubts. You are a new creature in Christ.
Jesus died and his blood paid for your sins. That blood is important..if evil is plaguing you just affirm Jesus blood paid it all. Not just his death, for Satan could say 'everyone dies, so what?' but Jesus own blood shed for the sins of the world.
James letter says if you lack wisdom ask God and he will give it to you generously but you must ask in faith and do not doubt. He says a double-minded person is unstable in all his ways and won't recieve anything of God.
When I read this verse I knew it was true and that I had to put away everything I was following that was not of God, because I did not feel strong in my faith. I wanted to know why my mind had been so troubled, but the Holy Spirit led me to this verse. As you came from atheism you may have been following man-made philosophies,..I know I was, and this confused my mind. I confessed to God I would now only serve Him and he gave me peace and strength. I had to cast down every argument that opposed God and bring my thoughts captive to Christ. (this mean a lot of Bible reading for me!)
Do you know about the armour of God? Read the letter of Ephesians 6:11
Finally, my brethren, be strong in the Lord, and in the power of his might. (11) Put on the whole armor of God, that ye may be able to stand against the wiles of the devil. (12) For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places. (13) Wherefore take unto you the whole armor of God, that ye may be able to withstand in the evil day, and having done all, to stand. (14) Stand therefore, having your loins girt about with truth, and having on the breastplate of righteousness; (15) And your feet shod with the preparation of the gospel of peace; (16) Above all, taking the shield of faith, wherewith ye shall be able to quench all the fiery darts of the wicked. (17) And take the helmet of salvation, and the sword of the Spirit, which is the word of God: (18) Praying always with all prayer and supplication in the Spirit, and watching thereunto with all perseverance and supplication for all saints; [
I pray you be filled with the Holy Spirit and stay strong against Satan by putting on this armour. When you resist him, he will flee from you. Jesus has authority over Satan and that means you have authority as well. Pray in the name of Jesus.
If you have not previously been baptized I would suggest you ask at your church to be baptized..if you already have, just affirm that you have been baptized into Christ, you buried your old self with Jesus work on the cross, He rose again and you rose again to new life.