It is not advised that you take a home pregnancy test until after you know you've missed your period. Although the hormones are present, the tests are not really guaranteed so early as 2 or 3 days after becoming pregnant. On the other hand, if you've missed a period and you are in fact pregnant, the home tests are 99.9% right. Normally, a pregnancy test gives a false negative - but rarely false positives.
If you've ever been on birth control and had any side effects from it, pregnancy often mirrors those side effects. For example: many women who suffered from migraines while on the pill begin getting migraines again when they become pregnant. If you are going to experience morning sickness it usually starts right away. Even without the nausea - pregnancy brings an almost immediate heightened sense of smell and aversion to many smells that never bothered you. Another early sign of pregnancy is frequency of desire to empty your bladder - even though it is not full.
Again, all of these things typically do not show up until after you've missed your period. If you are late in starting, take a test. If it is negative - you might want to re-test or see a doctor for a second opinion, but if it is positive you are probably pregnant.
Most females become suspicious when they miss a menstrual cycle, they are "late" with the monthly event. Some women experience slight spotting, this may be a clue. Other women report that they have an abdominal sensation that is out of the ordinary.
You can always go get an over the counter home pregnancy test and test your urine, or you could go see your doctor. Commercial home pregnancy kit's test for a hormone in the urine that is only present when the female is pregnant. This hormone is called beta HCG, human chorionic gonadotropin. The hormone is present in the urine about two to three days after the female becomes pregnant.