If you are taking the pill on time and schedule, then you shouldn't have any more chance of becoming pregnant because of the bleeding, but you should discuss this with your gynecologist. Unexplained bleeding should always be investigated. What the correlation is between sleep and breakthrough bleeding, I don't know. Stress may be one possible cause.

Merely Me, a writer for the site wrote an article about, Bleeding In Between Periods: What does it mean? This might be of interest to you.

The following was taken from Drugs.com's information about Ortho Tri-Cyclen, Section 11, I don't know what you are currently using:

"Breakthrough bleeding and spotting are sometimes encountered in patients on oral contraceptives, especially during the first three months of use. Non-hormonal causes should be considered and adequate diagnostic measures taken to rule out malignancy or pregnancy in the event of breakthrough bleeding, as in the case of any abnormal vaginal bleeding. If pathology has been excluded, time or a change to another formulation may solve the problem. In the event of amenorrhea, pregnancy should be ruled out.

Some women may encounter post-pill amenorrhea or oligomenorrhea, especially when such a condition was preexistent."