The speaker opens by taking all the blame, repeating "I'm the cause" as if it were a fact she has stopped questioning. The short lines then show what that guilt does to her body: she can't eat, sleep, or breathe, and she isn't happy. Pain and self-blame seem tangled together.
The second half shifts to a list of demands, probably the voices she hears from other people or from society. Many of them contradict each other. Be tough like a guy, but dress like a girl. Act like a child, but be mature. No one could satisfy both sides, which is the point. The poem ends on "No less than Perfect," with the final word capitalized, as if perfection is the only acceptable result.
The mood is tight, anxious, and exhausted. The clipped, plain lines feel like a person running out of breath, trapped by expectations she can never meet and punishing herself for failing.