Everyone around the speaker believes things have improved, and the speaker is quietly correcting that. The opening line sounds like an observation, but the sharp "I haven't!" that follows breaks through like a confession the speaker has been holding back. What has actually improved isn't the pain. It's the skill of covering it up.
The poem is built from short, plain lines, and that simplicity makes it feel raw. The speaker describes putting on a smile and laughing, the outward signs people look for when they want to believe someone is okay. Then comes the turn: "But deep in my heart," followed by words like "aching" and "hurting." The broken, stop-start rhythm feels like someone struggling to say it out loud.
The mood is sad and lonely, but also a little urgent. The final question, "Don't you know?", reads like a quiet plea to be noticed, and the closing "I am in pain" states the truth with no disguise left.