Changed O dates

My glow app said I was ment to O today on the 12th so we BD on the 11th the best day to BD but now it has changed dates, I'm guessing it's due to me entering my information. I've never tracked my opk before this is my 1st month tracking and according to clear blue digital I haven't O yet but my period is always 29 day cycles so will my period change also this month or could I O and still have my period due on the 26th? And does this mean now we need to BD today the 12th?? Or will it change again??

Has any1 else had there days change and wat did u do?