Spotlight indexing issue

Hello,

I have a macbook pro retina late 2013. I have added a micro SD card to it. The spotlight search doesn't return any results from the SD card. When i reindex, it starts to search within the SD card and i get results in spotlight but after some time, if i put the lid down and open it again at a different time i find that it is no longer searching in the SD card again and i have to reindex for it to work again

I have tried to find the indexing file to see what happens to it (does its size change etc) using the below command:

sudo du -m /.Spotlight-V100

But the command returns:

du: /.Spotlight-V100: No such file or directory

I am unable to get my spolight to work on the contents of my micro SD card. Any help would be appreciated

Thanks