I felt real tired. This is not uncommon. As long as you do not have a fever and as long as the bleeding is not greater than a normal menses, the doctor will probably just have you wait to see what happens further. Probably not although sometimes strenuous activity can start off some spotting. It probably is not a menses but it could represent your first ovulation if you are not breast feeding.
Sexual relations can sometimes start up some bleeding postpartum for the first one or two times.
If it happened more than that you might need to see the doctor for a checkup. Now, my bleeding has changed it turned bright red with a few small clots. Could be but probably not. What tissue does come out sometime later is the decidua which is the tissue between the lining of the uterus and the placenta. It takes awhile to totally slough out.