I have been on the same pill for over 2 years. I missed one pill and took it 12 hours later than usual. That day I had light spotting. Later that week I had unprotected sex with my boyfriend but he pulled out and never ejaculated inside me. Ever since then (about 3 days after I had sex) I have been having brown discharge mixed with spotting for almost a week. I looked up implantation bleeding and it says that sound only last a day or two so I don't think that's it. However I am experiencing back pain and my period isn't until next week. Could I be pregnant?