Why can't I see the International Space Station the coming ten days in my neck of the woods? [Details inside].

Some weeks ago, in Greece, I saw, what I thought was a shooting star.
It turned out to be the ISS (I checked it on Internet).
After that I downloaded an app for my phone, an app that tells me when and where (which direction) the ISS is visible.
About ten sightings were announced for the next few days.
Later, when I was back in Holland, also a few sightings were listed.
Now, the last couple of days no possible views are being shown (also not for the next ten days).
My question: Since the ISS is orbiting Earth, why is it that sometimes it is visible three times a day (night), and then suddenly it not visible at all, for days/weeks?