you have not mentioned your current age. in the childhood the reason could be due to adenoids
[ mass of lymphoid tissue present behind the nose ]. and in summer due to excessive dryness with in the nose which can cause the blood vessel to open up and cause bleeding. if you are not having symptoms of cold
then you can use a short course of oxymetazoline
two times a day along with pseudoephidrine 60 mg two times a day for week. and if the bleeding still persists get an x-ray of paranasal sinuses
[pns] and the routine blood investigation to be done to rule out any other problem.