I think i have a large clump of mucus is stuck in my nose and i can't get it out. i can see the clump moving freely way in the back of my nostril.?

Sinus Rinse: If you can't blow it out, consider going to any pharmacy and picking up a neil-med sinus rinse kit. If it's really not a polyp or some other soft-tissue mass, then i'd expect you could rinse it out with the saline solution. Or, you could use an infant bulb-suction device to suck it out.

Likely a polyp: If you can't blow the mucus out and you can see it... It's probably a large polyp... Best to see your local ent.