In just four lines, the speaker describes a quiet struggle between how they write and how they feel. The "sensible pen" suggests a careful, practical way of writing, one that keeps things in check. But lately it has been "making things little," shrinking experiences down to a manageable size. Given the title, "Keeping it real," that shrinking looks like an attempt at honesty or restraint, a refusal to exaggerate.
Then night interrupts. It "wrote me / a multitude of aches," and the grammar flips: the speaker is no longer the writer but the thing being written. Pain arrives in the dark, in large numbers, and doesn't obey the pen's modest scale.
The mood is hushed, weary, and a little wry. The speaker seems to admit that sensible, small language can only hold so much, and that the body or the night has its own, much bigger, say.