Is it something wrong with my airbrush, or compressor or just me?

thats the great thing about this forum ! 

Thanks guys. It's really good to get help promptly.

First, the Paasche H is an external mix airbrush.  That type of airbrush will always have a coarser pattern than an internal mix airbrush.  Next, acrylics dry very, very quickly.  The most likely cause of your problem is that the paint is partially drying in the air between the airbrush and the model.  Twenty psi just makes that worse because you are probably holding the airbrush a lot farther from the surface just to keep that high pressure from splattering the paint.  Try adding some acrylic retarder to your paint mix, reducing the pressure to no more than 15 psi (I prefer 12 psi) and getting no farther than 6" (I prefer 3" or so) from the surface of the model.

You could try straining your paint.  That might help too.

I don't know the circumstances but is your paint thinned properly? Have you cleaned your airbrush really well? Have you lubed your airbrush after a good cleaning.  Greg