Sitemap for a custom coded website

Hey I have a custom coded website but there is a problem that my post does not get added in sitemap automatically, Is there any script already build-up by someone which I can use so it automatically updates the sitemap. Otherwise, I have to add manual time every time I add a post in my website. Here is my website link

I would try this out:

Then you can use something like https://www.phpjobscheduler.co.uk/ to get it to run automatically.