It sounds like it could be burnout.

Nevertheless I de-facto recommend you read "The Practice of Programming" by Pike and Kernighan. I would also you recommend learning how to learn (there is a good coursera course on it), and also I would recommend finding a good course on learning to search for things.

The last two things are probably more important that having "good knowledge" -- being able to find the good knowledge, and good sources, and knowing enough to discern bad knowledge from good.