I Am Taking Cerazette For The Last 3 Years And

I am taking cerazette for the last 3 years and have since had irregular bleeding and can never tell exactly when my period is due and especially the last 3 months it's now 36 days since my last period . Anyway I'm going on holidays tomorrow for 2 weeks and was given primulot to delay periods while away .Feel like I might be going to get my periods is it too late to start taking the primulot now to stop them ?? TIA