Forgetting to take Birth Control, possible miscarriage?

I have been taking Birth Control for over a year now. In the last few months I have been purposely skipping my period using my birth control, My doctor told me it was safe. This past month I was never really consistent with taking my pill at the usual time due to working days/nights, more then once I forgot to take it on the proper day. On the last couple pills I started spotting so I stopped taking them completely, I thought I was going through a normal period, but it is very dark, and today I noticed a grey disc shaped tissue, it was not a blood clot, it was rubbery and tough, I don't think it could have been torn in half. And it was very noticeable. Was this a miscarriage? Or was it because I wasn't letting myself have a period? I had no Symptoms whatsoever of pregnancy, and I did not experience any unusual cramping or pain during my period. Im a bit confused, any enlightenment would be greatly appreciated. Oh, and I haven't been ually active in at least two months if that helps.