Betta fish doesn't eat at all

I have a betta fish that I purchased 2 and a half weeks ago. It is in a flat sided bowl, i am changing the water weekly. Since I've got it it did not eat. The food that i have is the Wardley betta prerimum food. When I asked at petco what to do, they suggested to try the bettafix drops. I've tried it for 7 days, still It's seems like nothing helps.
The fish is inactive(from the begnning)still alive but I'm affreid that not for long.
What else can I do?
Thank's

I have been told that wardley isn't a good company for betta food. You can try frozen bloodworms. Most bettas usually love these. By flat sided bowls, is it those small bowls which only hold like a pint of water? Those fluctuate temp. and water chemistry easily. I suggest you keep a betta in a tank of at least 2.5 gallons to house one comfortably.

try bettas flake food, they work alot better for some new bettas. my friend got one and at first it only like flake food and den it got accustom to pellets, also wat size is da tank?

try a 2.5 gallon or more, even though they can live in small tanks doesnt meen they like it!!