sounds like what happened is you had a virus that was pretty bad but then turned into pneumonia, so it wasn't necessarily a missed diagnosis. It's possible your roomate has caught a similar virus but they are putting her on antibiotics just in case. Another possibility is both of you have caught a different virus with similar chest symptoms causing you to not feel any better. In either case definitely get a follow up chest x-ray. If it's clear, then unfortunately you just need to ride it out as it takes its course.