The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

I have pain radiating from my navel
to my lower right ABDOMEN.
The Big Bang Theory Season 4, Episode 2

...will not keep testicles in your ABDOMEN.
The Big Bang Theory Season 8, Episode 23

is causing my testicles
to take cover in my ABDOMEN.
The Big Bang Theory Season 11, Episode 8