Last month my wife had menses only for one and a half day. This month she didn't had menses. We did urine pregnancy test and the result was negative. But still menses didn't come. After one week we again did the test and the result was null. The next day we again did a urine test and it also resulted in null. Although evrytime we took a new device for test. She doesn't want to get pregnant. What should we do to avoid pregnancy. Please help. Menses time is between 10 -15th of the month. Should we wait for next month.