My ex gf hasn't had her period in 3 months. she took a pregnancy test last week and one this week and both were negative. shes been very stressed ?

Irregular menses: Irregular menses are very common in young women, especially those under stress (who isn't?) and/or complicated by anovulatory cycles. It's very unlikely to be pregnant after 2 negative tests performed after late menses. Birth control pills are often used to regulate irregular menses. If you're not prepared to become a father yet, be sure to wrap it up every time (wear a condom). Prevents STDs too