Thanks for writing to H.C.M. for your query.
I have gone through your query regarding yellowish phlegm comming out from left nostril
and white from right nostril.
Considering your symptoms and history of illness of last 13 days it appears that most likely your left sinus has got infected thus oozing out yellowish phlegm. To confirm it and to manage it you should do following investigations-
(a) C.T.scan of paranasal sinuses
(b) Culture and sensitivity of phlegm from left nostril.
By this much work and through examination of nose and sinuses one may reach to correct diagnosis and accordingly treatment may be planed .