My Husband And I Have Been Having Unprotected Sex For

My husband and I have been having unprotected sex for a few months now my last period was oct 27-nov 3rd. Since then we have had intercourse quite a bit. Recently on dec 8th I got what seemed like my period. It lasted only a few hours. Which was weird. The tampon seemed to have some new blood but also old blood and it wasnt full. Since then I have had a bit of cramping, slightly tender nipples and i have felt nausea but have no vomiting. Could this be anything?