Bad feeling in the heart

I have, in these last days, felt a bad feeling in my heart. Let me explain so you can insha a Lah, with the Quran and Sunnah, explain it to me. So these last days, when I say the shahada, I feel like my heart is not safe, and that there is shirk being committed in my heart. Is this a sign of kufr or shirk and what does it mean in the Quran or Sunnah.