Could i be pregnant even if i had sex august 13 and on august 14 i had very light irregular period?

Of course: Anytime you have intercourse without protection there is always the risk of getting pregnant. That was two weeks ago though so the easiest thing to do is to check a home pregnancy test. By now the result would be reliable. Once you do the test you will know your answer. If you do not desire pregnancy please schedule a visit to discuss more effective types of birth control.