Somethimes i blow my nose something black comes out also when cough comes out from mouth?

See your doctor: Problems like these can only be correctly handled by your doctor in person. He/she needs to listen to you, perform an examination and possibly run labs or other tests. That's the only way he/she can find out what's going on and what to do about it.

Environment?: Could possibly be something from school, work or your surroundings. If you live in an area with allot of industrial smoke stacks, wood burning, etc this may be the cause. Look to the simple things first.

Try this first: Try a week or two of using an over the counter salinse sinus rinse. This a salt water solution one would use to flush out the sinus cavity. See what happens (does it get better?). If it continues after doing this, its time to see your local ent. Also sometimes, old blood in the nasal passages can become very dark almost black.

Few possibilities: 1. Environmental causes from smoke, fumes, dust inhalation 2.Tobacco inhalation can cause. 3. Sinusitis- acute if bad enough or chronic- causing death of superficial sinus mucus linings & coming out as black stuff.4.Chr.Nose inflamm. 5. Rarely fungal infections though unusual for your age/occurs in imm. Supp-pts- mucormycosis 6.Marihuana inh .See ENT doctor if not from smoke/dust.Mask helps if envir.