Do I use the word irritable or irritated for this sentence?

Both are correct. 

Irritable typically means you feel upset, but may not have a specific cause. "I feel irritable today."

Feeling irritated typically has a cause. "I was sound asleep when my neighbor started mowing his lawn at 7 a.m. I am so irritated about it."

Irritable is to be in a bad mood and easily irritated. 

If you're feeling 'irritable', you're ready to be irritated. You're on edge, you're in a bad mood, and you're just waiting for something to irritate you so that you can bite someone's head off.

If you're feeling 'irritated', then something has ALREADY happened to irritate you.

It depends on what you actually mean. They are NOT synonyms

It may fit better if you got rid of "feeling", such as: I'm so irritated right now. I would forget the word "irritable" because that means you are capable of being irritated, but may not be there (irritated) yet. Another option is: I'm very irritated now. Further, if you want to forget irritated completely, consider alternatives like: displeased, upset, etc.

depends. are you edgy or ticked off?

Both are correct, as far as I know,both are adjectives having the same meaning."irritated"is past participle adjective.I feel worried now for having lost my book.Here "worried" is past participle adjective

Both are correct. “Irritable” means “can be easily irritated”. “Irritated” means that it has already happened.

Irritable means easily irritated. So you feel irritated, and you are irritable.