Lower abdominal, lower back, backside and left side near hip pain after eating

Hi,

I hope someone can help me.

For the last week i have had an excruciating cramping pain just under my belly button, my lower back, my backside and left side near my hip after eating. It doesnt matter what it is - a piece of chocolate, a meal, a sweet. The pain is incredible. When i straighten my up body the pain lessens, but after the pain has gone my belly feels very sore and the left side feels numb. It hurts to walk. I feel very nauseous as well.

What could it be?

I thought it could be something i ate not agreeing with me.

Thanks xx