Hi..
Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concerns..
As per your complain blockage of one nostril can be due to causes like Nasal Polyp, sinus congestion or 
Sinusitis, deviated 
nasal septum, allergies etc..
It needs a proper evaluation for a correct diagnosis..
I would suggest you to consult an Otolaryngologist and get evaluated and a Nasal endoscopy and x ray of sinuses can help in diagnosis and treatment can be done accordingly..
In case of Sinusitis a course of antibiotics, anti inflammatory painkiller, decongestant Oral and nasal drops, steam inhalation can help..
In case of nasal polyp Steroid 
nasal spray, Steroid injection in the polyp and if dies not work surgical removal is advisable..
In case of 
allergic reaction anti-allergics like Levocetrizine and nasal decongestant can help..
In case of deviated nasal septum 
Septoplasty that is straightening of the septum to increase the nostril space can be advised.. 
Hope this information helps..
Thanks and regards.
Dr.Honey Nandwani Arora.