Bottling question

I have recently started drinking some of my last batch of brew after three weeks in the bottle. The beer in the glass bottles are great, the ones in the pepsi bottles are flatter and have an off taste.
I was wondering if the plastic bottles have absorbed some of the pepsi flavour and is now releasing it into the beer.
Also I was wondering if the larger bottles need more time to carbonate than the smaller ones.

Thanks.

Yes and yes. Pepsi is not as bad as root beer but some of the flavor may have lingered. Larger bottles can take a week or so longer.

wow, thanks for the quick reply.
Good to know, I will the plastic out of the fridge and put in the glass.

Carbonation happens because the CO2 has nowhere to go except to dissolve into solution. I wonder if plastic gives/expands slightly, requiring more CO2 to acheive the same perceived carbonation level.