Hi Fatema, I was facing the same problem with my website.
The problem was someone had access to my account without my knowledge. Here’s what I suggest:
1. Remove all users that have administrator access. (Only keep yourself)
2. Install “WordFence” plugin. And activate 2-Factor Authentication for your user account.
This would restrict access to anyone who is using your website to host spam posts.
This could also be malware, so you should do a scan using WordFence. While malware removal is a tricky task, this should stop the spam posts for now.
Let me know if this helps!