Sounds like something I went through a few years back. Satan attempts to place DOUBT and FEAR in our minds. The antidote was to press closer to God by focusing on Jesus, who banishes all doubt and fear. For me that meant increasing time spent hearing the Word, which is the same as spending time with Christ. And praying. Lots of speaking with God.
Satan can chew Brimstone
He will have eternity to Digest It !