pools measure your current performance by frequency of accepted shares, this can easily swing by double digit percentages for small workers like yours. Check again some other time, maybe you'll see 20mh/s
also wtf are you doing mining on a gt 730??
And to add also, you can always contact
ocminer if you need some help or doubts. He's the owner of suprnova and trusted guy here. So no need to worry about such "stolen hashrates". Been using his mining pool before also.