witching hour???

What exactly is it? Ds is 2.5 months and at around 5 pm he always starts fussing. It's not uncontrollable crying exactly but just constantly fussing non stop I do everything possible. Carrying, laying down, baby wearing, white noise, nursing him, pacifier, shower. Nothing helps for more than a few minutes. Is this normal what could it be.. I'm getting so frustrated and exhausted. Help tips ideas anything.