My 5 Year Old Grandson Has Had A Bad Dry

My 5 year old grandson has had a bad dry cough & stuffed sinuses for 3 weeks. Now it has gotten bad enough that he coughs until he can barely catch his breathe & his nose starts pouring blood & big clots of blood comes out of his nose & he feels like it's in his throat too. Is this just an allergy or sinus blockage or serious?