I've been using Elementary OS daily this week and every day there is a update in the app center.
The update just appears as operating system updates
Is that normal?
Yes, that's quite normal, usually it's "upstream" packages. The next version of the AppCenter will show more details on those Operating System Updates, see: https://github.com/elementary/appcenter/pull/518
When you've added third party ppa's you'll also get more frequent Operating System Updates since those updates are not listed separately in the AppCenter. (I'm not sure why)
To see more details on the updates, without the next version of the AppCenter you could run the following commands in the Terminal:
sudo apt update
apt list --upgradable
To get more information on a specific package you could run:
apt show packagename
