I am 157cm,i.e. 5feet 2 inches
I apparently have a straight figure
Bust size;35
Waist(now) 31
Hip 36

I would say what you have now is pretty good. Why do you think your waist is the wrong size?

I still look chubby and am overweight. My dietician suggested to lose more weight... :p
I want to have a small frame sized waist :(
I'm not confident about my waist size cause I took the measurements alone

There are several minds about this, and this is my opinion.

Based on several studies and ancedotal evidence, body fat isn't as dangerous as we're lead to believe. Being over weight is a concept that is different to everyone and there is not one true standard to say that one person is healthy or not. A person can be obese and be healthier then someone who is the ideal weight.

Based on free web apps, you are okay to should consider doing something. What that is is anyone's guess. You might be a little chubby, but that isn't a bad thing. I think your selfimage here is more to blame than your actual body shape. You're not confident in your body regardless of your size, so being small framed will not solve that issue.

What can you do at this point? Eat well and exercise. Make sure that you're expending more energy then you're taking in WITHOUT starving yourself. Your diet should be balanced and should be nutritious. When it isn't your body will go into a starvation mode and you will actually start to gain weight. You need to convince your body it is healthy and has an abundant amount of energy and sustenance.

As for exercise, start slow and build it up. If there is a gym nearby, go to it and consult a trainer.

Thank you CravenMorhead, but I want to be small framed because of several reasons, here are some; I have a treatment coming up which requires me to lose a couple more kilos because my weight makes me get pimples, my guy is really skinny and I want to get skinny so that we look good as a couple :p , there are a couple of dresses which make me look real skinny and I look awesomely beautiful and sexy when I look skinny! Moreover,my guy,my friends and relatives want me to lose weight and be sexy :P