[REM]

If I'm not mistaken wait until you see blooms. At that point tiny potateos are forming and new potatoes will be ready in a couple of weeks.

That's from my mom who has gardened all of her life. I'm doing my first potato crop right now and I noticed a few blooms yesterday.

Potatoes are a full sun crop, so I doubt that you had too much light.

 

[REM]

Ease up on the fertilizer. Taters need some, but too much will force vegetative growth over production of potatoes.

I'd suggest going to a feed and seed store and buying seed potatoes that do well in your area. I can only grow reds here. Other varieties fail.