はら　へった or おなか　すいた We usually use はらへったぁ or おなかすいたぁ

The correct about what you wrote is, as Jordan said, はらへった but I'd like to recommend you not to say so, it sounds a bit boyish though there are many girls use it in everyday conversation. The better is saying おなか(が)すいた 。(*In colloquial, you can get が off.)

Double consonants are all written with a small tsu character before, so for example: った(tta), っか(kka) and so on.

飢えた = うえた