Hi..
Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concerns..
As per your complain Nasal Polyp is over growth of 
soft tissue inside nostrils and hangs inside nostrils and is seen commonly in cases of chronic infections like 
Allergic Rhinitis, 
Chronic Sinusitis,Chronic cold or respiratory infections, Asthma etc..
It can very much occur in a single nostril..
But for confirmation that it is just a swelling or a polyp a clinical examination is a must..
When it is small it does not generally causes any problem but when it is increased in size it can cause breathing obstruction due to obliterating the nasal passages..
I would suggest you to consult an Otolaryngologist and get evaluated and a thorough clinical evaluation and nasal 
endoscopy..
You can be advised 
steroid nasal drops that will help in shrinkage of the polyp..
In case if there is no resolution surgical removal of polyps can be done..
Hope this information helps..
Thanks and regards.
Dr.Honey Nandwani Arora.