I have really bad nausea. I can’t eat anything. Also stomach cramps.
我還特別惡心。什么都吃不下。還有胃痙攣。

Nausea
反胃

Nausea is a type of sickness where you feel like you are close to vomiting.
反胃是你感覺自己要吐時的感覺。

Her nausea was so bad that drinking water didn't even help.
她反胃得非常厲害，喝水都沒有用。

Nauseous
惡心的

When someone feels nauseous, it means that they have nausea.
當有人覺得惡心，就是說他們在反胃。

If you have nausea, you can say: "I feel nauseous." or "I have really bad nausea."
如果你反胃時可以說“我覺得惡心”，或者“我反胃非常嚴重”。

Stomach cramps
胃痙攣

Stomach cramps are where it feels like your stomach is being squeezed really tightly.
胃痙攣是你感覺自己的胃都絞在一起。

When she got her period, she would have very painful stomach cramps.
她大姨媽的時候胃痙攣非常嚴重。

Stomach cramps are a feeling of your stomach being squeezed.
胃痙攣是你覺得自己的胃絞在一起。

Stomach aches
胃痛

A stomach ache is just an overall soreness in your stomach.
胃痛是胃整個很痛。

I'm not surprised he got a stomach ache after eating all of that pizza.
他吃了那么多披薩，怪不得會胃疼。