I read that the cukes need to be harvested before they turn yellow but my cukes are turning yellow before they are a good size. It starts from the bottom of the cuke when it is very small.

I let a few get big but the yellow continued up the cuke.

I harvested 2 to see what they tasted like. The part that was green was alright but the rest was bitter.

What am I doing wrong? I have no idea what variety they are either.They are yellow by the time they are about 4"s long