Is there any thing which makes our skin white and stops melanin

You mean to enlighten the pimple marks, well I think Nomarks is a good product there. But if not, then you can try chandan powder with rose water. But if you also tried this out, then why not consult a dermatologist so that he/she can give you proper topical medication plus oral medication too if needed. There are lots of skin whitening in our country, i don't know if your interested in whitening pills. You can pm me here in mylot if you want to know the details. This product will depend on your metabolism also. Products work depending on the shade of the skin you have. The best and less expensive I can still give you is fruits. Eat fresh fruits and green veggies. Do not take much on milk and dairy products that is why you get those acne or oil. Lessen the meat intake also. And avoid eating fried foods and junk foods. There are also whitening lotions you can apply, but you need to do this together with whitening soap and the whitening pill that is suitable for your skin.