What Causes Thick Mucus Discharge From Throat Upon Waking Up?

Hi, I feel like there s a hole in the left side of my throat and it hurts sometimes but doesn t stop me from eating or drinking anything,but every mornings or any time I woke up from a nap I feel like I have to clean my throat and there would be something like mucus but thicker coming out of my throat please tell me what can cause this.