Your chemist will help you with a choice of product. Many have private areas for consultation or you can pass a note to the chemist describing your symptoms and he will discretely let you have the medication you require.
There are a couple ways you can self diagnose. If you are itchy and the discharge looks sort of clumpy or frothy, it is probably a yeast infection. It really is best to see a gynecologist when you have these problems, because a lot of women treat for yeast infections without actually having a yeast infection. I don't know if they are available to you where you are, but the brand AZO makes a yeast infection test kit, and there might be other brands out there. You should speak with a pharmacist if you need help with these products, but personally I prefer Vagistat 1. I like being able to do something once and not have to keep repeating treatment, in case I forget. Good luck!
Most likely you have a yeast infection if it was something else it be yellow. So don't worry just seek a gynecologist so they can give you the topical that you insert and that should work.