Not all are like that. My sis works as a pharmacist. What are the areas that u would like to know ? She would be glad to help u out 

I hope your sister is not one of those pharmacists who recommend Vitamin C tablets to those having the cold/flu.

Currently I'm taking vitamin C to prevent flu and cough.

Ester-C which is 1000mg per tablet per day.

Rather than taking sore throat , flu medicine .

Just something to prevent this simple ill

It's not even needed for prevention. Supplements such as Vitamin C, B, D, etc. are only for supplementing any known deficiencies, until a solution has been found as to alleviate that deficiency. If you are truly lacking Vitamin C in your diet, it can be easily concluded that you are having a real bad diet that is deficient of a whole lot of other vitamins too. By taking your regular vegetables and fruits as part of a balanced healthy diet, you don't even need these commonly touted supplementations. Of course, there are certain other essential nutrients that are hard to find in everyday diet, now those are worthy of some supplementations.

If you wanna put it that way there is also literature supporting that consumption of ascorbic acid, and other chemically/artificially derived supplements will do more harm in the long term than any good. Many common health problems usually stem from a poor diet over anything else. An organic guava a day provides you with guaranteed benefits, as opposed to the questionable effects of ascorbic acid, plus a whole lot of other vitamins and minerals.

Forgot the sites but the book Supplements Exposed by Dr Brian Clement is a good place to start your search.

In your case if you're really worried, try radically changing your lifestyle and diet, adopting the following:

Paleo diet (see Mark's Daily Apple)
Mindfulness based meditation (see Deepak Chopra, Richard Davidson, Matthieu Ricard)
Regular exercise (see Dr Mercola's Peak Fitness Program)

Note to critics: The list of reference above doesn't indicate an advocacy of belief system, rather, an easy reference point for many of the core choices made therein, which are undoubtedly beneficial.

Once you get the above in order, then look at your available financial budget and determine what supplements you should be taking to tweak your health and play around with science to optimize your daily life experience. Consider family history in the selection process.

Seems as though you're in need of some meditation classes 

Well in that case the book should serve as a primer for judging what's good and what's bad for you in terms of supplementation. By the way for reference the forumer named Tham here has some really good knowledge on the effects of many herbs and supplements for particular conditions. Perhaps you can gain some knowledge from him there if you're interested.