I find my sandpaper gets gummed up with poly quickly...
That's a sure sign that the poly is not fully set. Depending on how many coats have been applied, how much they were allowed to "dry" between coats, ambient temperature and humidity etc... you may need to leave it for at least 4 weeks before sanding at all.

As I said before, finishing is not a race or an easy task for the impatient. (and I definitely fall into that category!)