It look like this?
My female is pretty big and looks bloated, but is eating very well and mates.
It very well could be a female, as they are bigger, and is just an older fish.. mind you, tigers can get up to 3inches big.
I think that you just got it, its prolly stressed out. Get some aquarium salt and dose the tank once and keep the light photo period to only feeding time - twice a day and small amount each time. They dont require alot of food.