What Causes Delayed Periods?

good evening sir .i am a girl of 23 yrs old......my periods date was 4rth jan but till now my periods hav not came... i am very tensed....becoz before 10 days i hav done orally sex wid my partner ....but nothing do any physically relation. pls help me sir , i am very tensed abt it ... becoz my periods are delayed to 4 days .....