[Always *]

You can get prenatal vitamins over the counter at many grocery stores and pharmacies. Taking them even if you aren't pregnant is not harmful, I know this because I have seen/heard multiple times that many women try to plan ahead by taking the vitamins ahead of time to build up the necessary amount, I don't think it is critical, it's just encouraged for women who are planning a family. Any who, my point is that the vitamin is perfectly safe to take at any point during a pregnancy (even before hand), so I'd start there.

It'll be ok to wait until Monday to get the formal pregnancy test. I know that finding out you are unexpectedly pregnant must be causing a lot of anxiety, but you must be early in the pregnancy so a matter of a few days won't make a huge difference (unless, of course, you are smoking, using drugs, drinking alcohol, etc., which you should discontinue). I think that a little coffee is ok, but I'd limit the caffeine.

It'll be ok. And congratulations, having a baby is a wonderful thing.