Is there a way to see all the TV shows I've watched or followed?

Yes, you could by using this link; http://www.tvmaze.com/dashboard/follows

Or click arrow down next to your name in the top right corner, click Dashboard. After that there is a tab 'Follow', which lists all shows you are following.

It is possible to watch it as well on the show page by using the filter; Following or Not following.

Thomas wrote:
Yes, you could by using this link; http://www.tvmaze.com/dashboard/follows
Or click arrow down next to your name in the top right corner, click Dashboard. After that there is a tab 'Follow', which lists all shows you are following.
It is possible to watch it as well on the show page by using the filter; Following or Not following.

How to see a list of watched show, if i don't click the button "following"?

You can only list shows that you're following, not shows that you've ever marked as watched. We do have plans to add this! (But we have quite some other plans as well..)