The speaker imagines herself buried alive inside her own sadness. Melancholia is her tomb, and she lies there waiting, not fighting her way out. The repeated "I lie" works twice over: she is lying down, and there's a hint that she may be lying to herself about how stuck she is.
What she waits for is spring. Jonquils blooming and starlings singing are small, ordinary signs of renewal, and she hopes they will be enough to lift her out, as if the world could do the rising for her. The title, "Exhume," fits this: to exhume is to dig up the buried, and she wants to be dug up by nature.
The mood is quiet, heavy and a little gothic. Hope and despair sit side by side. The last two lines, where her tears flood the crypt, suggest that while she waits, her grief keeps rising, and the tomb may fill faster than spring can arrive.