Miscarried- had no idea- feel guilty

I knew something was wrong with my period, it was two weeks late, and I was dizzy, nauseous and it hurt way more than usual. We only had sex once last month and it wasn't even my "fertile period" (so much for that), and while I'm grateful it "worked", I pushed myself very hard on client projects and my high school reunion (which I ran). I pushed my body very hard and now I feel guilty. I got sick during my reunion (which was either allergies or a cold), had a tremendous backache, which I ignored and stayed up late. I drank a good bit of wine with my dad the Monday before I left, and feel terrible now that I made it hard for my baby to survive. I had NO symptoms of pregnancy whatsoever. No bloating, sore breasts, nothing. 
Yesterday, I passed the placenta, and wasn't sure what it was. Now I feel terrible that I flushed it down the toilet. I'm a terrible heartless person! I'm not being careful enough! What should I have done! How can I take this process more seriously! I didn't think there was a chance I was pregnant, and feel awful. Should I have buried the placenta? I stared at it for a while and then flushed it down the toilet, and I feel like that was wrong. I was five weeks, so I couldn't tell what it was. My body aborted the baby, am I to blame? And how do people handle this?