Hello, I Was On The Yellow Pill Last Year. I

Hello,
I was on the yellow pill last year. I stopped using it due to not needing it. When I was in a relationship I went back to the doctors and asked to be put back into my pill, she out me on the purple pill, I had to go back to the doctors a month n half later due to being on for 2 weeks, she had Swapped me back over to the yellow pill, I had taken this straight away and has had sex while swapping them over. My partner uses the pulling out method and I am now a week late from my period. I had taken a test and it was negative. Could me be late for my period do with swapping my pill and the pill I'm on effect why I'm late?