I've been on BC for about a year and a half & I rarely missed any pills. I had recently started a new job last month and my schedule had been kind of hectic. I started a new pack of BC pills on April 29 and took all my pills for week 1 on time without missing any. During week 2 of BC, I had to stay overtime at my job for 2 days & it threw my schedule off so I ended up missing 2 days of pills. As soon as I realized I had missed the pills, I took 2 pills one day & 2 the next day to get back on schedule. I didn't miss anymore pills for that week. I took the rest of the BC pills on time without missing any for the remainder of week 2 & week 3. On the last day of week 3 (May 13) I had unprotected sex. What are the chances of pregnancy & should I go ahead & purchase Plan B just in case?