I Married A Dead Man by Cornell Woolrich

What if you woke up to discover everyone thought you were somebody else?

Pregnant and abandoned, all Helen Georgesson has is five dollars and a one-way ticket to San Francisco. Then she is involved in a train crash, and regains consciousness only to discover that she has given birth – and, in a bizarre twist of fate, has been mistaken for somebody else. Helen decides to claim this opportunity to make a new life for herself and her son. But eventually her past will catch up with her, in terrible ways…