I had my period on may 20 it l last for three days it wasnt heavy i had no cramps my period usually last up to 5 days could i be pregnant ?

Yes, it's possible: If you are sexually active, pregnancy is possible. The only way to know for sure is to take a pregnancy test. However, unusual bleeding during your cycle can be due to various reasons ranging from anovulation to pregnancy.

Not likley: If you had your period at the normal time, even if it was light, it not likely that you are pregnant. If you miss your next period, you could do a home pregnancy test. If you intend to be pregnant, please see your doctor so that s/he may initiate pre-natal care now, even before you may be pregnant.