How long after a chapter 7 can you file a Chapter 13.?

We filed a chapter 7 on our own because we could not afford a lawyer. We still can't. My husband was hurt and now we are way behind. I have tried to get work, but I haven't worked in 20 years since we first got married. Can we re-open the bankruptcy and covert to chapter 13 or how long after a 7 can you file a chapter 13.