5 months after rhinoplasty, I have a cold and mucus with blood?

Most likely it's related to a dry or irritated area along the nasal septum, but one cannot be certain unless it's examined directly. You shouldn't be worried, but you should be seen to determine the exact cause especially if it's persistent. No one can give you the definitive reason here because the physical examination is an integral part of the diagnostic process; therefore, it needs to be seen and examined directly I'm sorry to say. Best of luck.

This is very common and not to be concerning!There is an area on your septum typically that has a grouping or plexus of blood vessels. Everyone has one.When it gets irritated from a cold or humidity change, it can bleed. Surgery makes this more common.The treatment is nasal salt water sprays (over the counter) and cold medicines. Don't use nasal decongestants for more than a couple of days.The mucus and bleeding should gradually go away.No exam is necessary unless it doesn't go away or it persists for more than two weeks.Hope this helps.Dr Chris Saunders

Even without a nose operation, bloody noses can happen from some trauma to the fragile nose mucosa. If the air flow is more turbulent than laminar ( smooth) then congestion can build up and the mucosa can become dry and more prone to bleeding. This is why you can get a nose bleed with a cold or after surgery or when it is dry or low humidity. I would have a nasal speculum exam to look into the inside of the nose and see if there is some obstruction.