The Multi-table Grind

Recently, I've been starting to play more and more tables of $5/$10 short on PP. The more tables I play, the more I realize that my money goes nowhere! I win a big pot at one table and I lose two small pots at another table. I make a few hundred, but then I get cleaned out at another table. Does anyone else experience this? Is this just part of the grind? It seems like the more tables I play, the slower I go up. Perhaps there's a hole in my game somewhere..