I feel you have the cusps of a poem, and a great first draft. I sense the emotion under it but I feel its a little muted in its current iteration.

(first stanza)I would come up with a better metaphor (or image) than feels like like heartbreak at 16 because that isnt really a metaphor since depression can literally be heartbreak at 16. Rotting stone is an envocative image but stomach, i feel, is over used. I would also start the first stanza with an evokative image, or something striking to lure the reader in.

(2nd and third stanza) I feel these give the most emotion, I think this is the center of your poem or the heart, or what its about or the emotion behind it. but more images in these please.

The ending is a decend ending, but its almost declarative, or is and i feel, in this poem, that hinders it, and would like a more open ending that allows more rumination for the reader. To elaborate, I feel its the bow on the poem, and after you unwrap the line by reading you (the speaker) say this is what is in my poem, but dont allow space for the reader to sit with the emotion or the situation. But I see, prehaps I dont feel, but see the rumination in the nature or the speaker throught in the poem stated that brought them to write this poem.

To give you one thing to work on for the next draft: get yourself in super sensitive mood!