Nasal Polyp/Cancer? Please help!

I have had some nasal congestion for the past few weeks. I only have it when I lay down and it changes sides when I flip.

It's only one nostril at a time.

Sometimes when I lay down I wont get congested at all but it's very rare.

My question is this ....

If it was cancer would the blockage change sides?

If it was sinus polyps would I only be congested when laying down and could it change sides?

When I flip I can feel something moving in my sinuses and blocking my nose.

Please help!