Insufficient Credit History?

so i've had a cell phone bill for about six months now and three months ago i got a co-signer and got a brand new truck, and before i had a car in my name, paying insurance on time, im paying all my bills and everything on time but every time i try applying for any type of credit card (Best Buy, Ebay, Walmart, etc.) i am denied and says insufficient credit history STILL, when will this change so that i can finally build up my credit and paying everything in cash, i mean i make really good money and im 19. i got approved $22,000 for my new truck but cant get $500 on a little credit card