What Is Stringy Clear Mucus That Comes While Spitting In Morning?

I USUALLY WAKE UP IN THE MORNING WITH THE URGE TO SPIT AND IRRITATION IN MY THROAT. SO I USUALLY GET UP AND BRUSH MY TEETH AND SPIT, I HAVE TO SPIT LIKE 3 OR 4 TIMES BEFORE I GET ANY THING OUT.. AND WHEN I DO, IT IS THIS STRINGY CLEAR MUCUS..WHAT IS THIS?? AND WHY??.. THIS ONLY HAPPENS IN THE MORNING AND AT NIGHT..