With a GX credit rating, will I ever get approved for a credit card? Any advice on credit rating?

I am a relatively new fresh graduate with about 6 months+ working experience. My monthly income is $2600 and occasionally have some commissions based on the nature of my job. I have tried to applied for 3 credit cards so far but all has failed once they ask for my CPF contribution. May I know if I will need a full year income in my CPF statement at least to apply for credit card? What does GX credit rating even means?