How early can a pregnancy test detect pregnancy????

So my husband and I got married on Aug 5th and we didn't start trying to conceive until Aug 6th. My breasts have been sore for about 3 weeks now and my period is really irregular so I decided to take a test (or 3) just out of curiosity but didn't really expect it to be positive since we haven't been trying very long. My question is...can this be right? It all happened much faster than we had expected?!