Hello
@Lenno, though we, as believers, have been given a new nature by God .. e.g.
Ezekiel 36:26-27; John 3:3; 2 Corinthians 5:17, our old nature/old man/old self is always nearby, ready to rear its ugly head and make a mess of things. We, in fact, will not be completely free of our "old self" (old nature) on this side of the grave, so we are commanded to put off our old self and put on the new, day by day, or minute by minute, as necessary .. e.g.
Ephesians 4:22-24, cf Romans 12:2.
Also, as a new believer, you need to have a growing understanding and awareness of the fact that you, like the rest of us, have a common enemy now (Satan and his demons), who whisper lies, deceptions and half-truths into a believer's ears (so to speak) to tempt us to turn from God by getting us to doubt the truth that He's given us in His word.
You need to resist him by taking such thoughts and feelings "captive" at the very moment that they enter your mind ..
2 Corinthians 10:5; James 4:7.
There is a book, a collection of short stories actually, by C.S. Lewis called,
The Screwtape Letters, that would be worth reading (if you have not already done so), especially since it is now free to read online (see the link above). The principal characters in the book are two demons, and it is from their perspective that Lewis writes his book (he first read each of the stories on the radio in England during the 1940's, if memory serves, and the collection/book is now considered to be one of our Christian classics
).
What this book will help you understand (even though it's fiction) is what the demons are up to/how and why they operate in your life as they do (so that you will be able to more easily and more quickly recognize their attacks for what they truly are and then resist them
).
One thing to remember is that since this book was written from the demons' POV, it is unlike any other Christian book that you will probably ever read (whenever you see the word "Enemy" in this book, for instance, you know that the Person being talked about is God). Be sure to read the Preface and any other intro material to gain a better understanding of it.
Finally, it would be a good idea to talk to your pastor and tell him what you are going through right now, both for his help & counsel, and so that he will know how he can be praying for you too.
Praying for you!
God bless you!!
--David