IF you are trying to have a baby, then all you can really do is wait it out.
IF NOT then you can get the morning after pill up to 5 days after unprotected sex, which prevents pregnancy.
Absolutely not.
Implantation spotting, if it happens at all, takes place between seven and 12 days after conception. That is how long it takes for a newly fertilized egg to travel down to the uterus and implant, which is what sometimes causes an implantation spotting.
Bleeding so soon after sex could be an ovulation bleeding, a bleeding from really vigorous sex during which your cervix was injured just a little, or a hormonal imbalance. It could also be an infection. If you are worried, see your doctor. If your menstrual cycles are irregular, it could also be an early period though.
no, it's not possible for the implantation bleeding to happen just one day after the unprotected sex. It's not even possible for you to conceive this fast - conception does not happen immediately after the ejaculation, but it can take up to few days for it to happen. Not to mention that you most likely were not ovulating this soon after your period.
This doesn't mean that you can't get pregnant from this sex, sperm can survive for a few days and you might ovulate early, but this just means that the bleeding you experienced was not the implantation bleeding.
Even though medical experts say that implantation cannot happen until at least 3 days after intercourse (and usually 6-12 days afterward) it is possible. I have 3 children. With every one of them I had implantation cramps 1-3 days after intercourse that lasted about a day. With one of them I had full blown pregnancy symptoms by the end of that first week. Professionals can give you the "average" results, but each person (and each pregnancy) is different. If you are in tune with your body you usually know what is going on with it. It is possible to have implantation as early as the next day.