Why do i feel like this?

On 1st May this year my gran died very suddenly, i was really shocked and upset, i went to see her coffin in the chapel of rest because my mum n dad didnt want me to c the body incase it upset me too much as it would of been 2 weeks after she died, we've had the funeral, and shes been cremated and is now in the cemetry with my grandad, but all of a sudden i feel like i havent griefed properly, like shes not really gone at all, and now i've gone off food almost completly cos i just dont feel hungry anymore, im not sure wat to do cos i dnt want this to effect my health, can anyone explain why i feel like this? im 17, and im 18 next month and having a party and i think thats when it will hit me most, but in the mean time what do i do with myself?