Hello,, I Am 25 Yrs Old . And I Want

Hello,,
I am 25 yrs old . And I want to delay my periods . My lmp was 17th april' 16 . And my last cycle was 45 days, but all the other ones have been exact 30days . I have my vacations planned on 19th to varanasi, so I want to delay my menses . As my previous cycle was irregular, I want to know when should I start taking regestrone and for how long . I want to delay my periods upto 22nd of may .