I would suggest you take these two tests and then follow up with a doctor for a full physical check-up.
The first test is the lab urine test.
This test can detect HCG in the urine with an accuracy of about 95%- and as early as 20 days after conception. Unlike the home test, it is performed by a professional, who is more likely to do it correctly. (of course, labs have been known to make mistakes , too.) If you plan on taking the test, call the lab the day before and ask for instructions on collecting your urine. This test is sometimes the least expensive pregnancy test, but it is less reliable than a blood test.
Or you can take a blood test, this serum pregnancy test can detect pregnancy with 95%-plus accuracy as early as 8 to 10 days after conception, and with virtually 100% accuracy (barring lab error) six weeks after conception. Now that they are in common use, blood tests often cost no more than urine tests, and their accuracy renders the necessity of a retest less likely.