Sensor keeps getting dirty

Hi all

I have a Sony A7ii.  I just came back from a trip.  Before the trip, I saw that the picture was showing small dots at f22.  So I cleaned the sensor and went for the trip.  During the 3 weeks trip (London/Paris), I did not change lens (since I only used 1 lens).  When I came back, I saw small dots again at f22.  The dots are gone once I increase aperture to f18 and so on.

Is that normal to have dust again and again or am I being paranoid?  I know that I don't use F22 a lot but I just don't fell comfortable that there are dots.

Note:

I changed the lens when I got back to see whether it's sensor related or lens related and the dots stayed at the same spots.