What Causes A Delayed Period After Slight Mid Cycle Bleeding?

Hi, last month i had my period like nomral then 7 days after i had another lighter one. IDk wht it is. I admit i had sex the day before the first period. my mom says its just hormones and i think its stress. I'm concered because i was expecting my next one and haven't got it yet i was wondering if my counting is off cuz my body changed. Help!