I see a lot of threads on experiencing pregnancy symptoms, and this may be beneficial for some.
Sore nipples, vaginal discharge, cramping, nausea, etc.
These are *all* symptoms of ovulation. During ovulation, your body is excreting a high level of hormones, similar to what you would experience in early pregnancy. Any of these "symptoms" should only be considered indicative of pregnancy if they are experienced at least 1 week after your period was due.
For most first time mothers, these symptoms can take longer to appear and come on more suddenly, as your body is not "accustomed" to pregnancy. This is why many first time moms don't know they are pregnant until they are 6-8 weeks along, but many "repeat moms" will "know" at 3-4 weeks.
Implantation bleeding
If you experience the symptoms above and they subside, then around a week later have a day or two of light pink-to-brown spotting, you may be experiencing implantation bleeding,
Implantation bleeding does *not* begin heavily and taper off. It also does not start off light and become heavier. All it is is the lining damaged/removed by the egg burrowing into the uterus.
Spotty bleeding that later becomes heavier, heavy bleeding that later becomes spotty, or bright red blood can be a normal, early period, or a failed implantation. Very rarely are these scenarios a result of "implantation" bleeding, although it is not outside the realm of possibility.
Hysterical Pregnancy
Sometimes, when some symptoms of pregnancy present themselves, a woman will unconsciously become "hysterically pregnant". The subconscious will being invoking other symptoms of pregnant, such as sore breasts, nausea or fatigue. This is quite common in women who think they may be pregnant and is similar to psychosomatic pain disorders, in which a small clue that could be related to a larger problem is followed to the expected end by the subconscious.
Long term "hysterical pregnancy" or "pseudocyesis" is a real medical condition, that often results in an exact mimicking of pregnancy symptoms, up to and including a "pregnant" or distended belly. "Hysterical pregnancies" can have such a strong effect on the body that in extremely rare cases a "hysterically pregnant" woman will test positive for pregnancy, even though she isn't pregnant. Women experiencing "hysterical pregnancy" usually miss periods for months at a time.