I am 21 years old gal... n my body secretes white fluid I heard of the term yeast infection.
I wanted to know if it's the same and how I can get rid of it?
The fluid has a odour,its is sticky and thick
And generally it is released before 10-12 days of mensuration date,sometime I also have itching in vagine but not in inner portion only on outside skin.
Some times in more amount and sometimes in less amount.
My weight is also less as compared to my height do this effect my body and weight to?

There are other infections but yeast is the most common, and your symptoms do match it. Any drugstore will have treatments, or ask for help selecting one.
If you get yeast often, it means your pH is off. Some women are able to keep it from recurring with diet, such as cranberry juice. Wear white cotton panties that aren't tight, and wash and bleach them after each wearing. Don't wear tight jeans/pants.