How To Delay Periods?

I had the contraceptive implant fitted in January of this year and my periods are still very unregular.
I am going on a sailing weekend in afew weeks and i want to know if there is a pill i can take to stop my periods over this time.
I know before i had the implant fitted my doctor could give me a pill to do this, but i'm not sure if this still applies.
Please help.
Thankyou.