Does having irreversible pulpitis automatically mean there is an infection?

Essentially, yes. Left untreated, an Irreversible Pulpitis will evolve into an abscess. That's when pain. and swelling can become unimaginable. You will then have only 3 choices: Fix it, Pull it or live with the pain!

Pulpitis = inflammation of the nerve inside the tooth. If the nerve is irreversibly inflamed the tooth needs root canal therapy, or extraction. No other choices. If left untreated you will wish it was treated sooner. If you have pulpitis it means the nerve is still vital, no infection. In the nerve dies from invasive bacteria, infection.