According to psychologist Mihaly Csikszentmihalyi, the human nervous system can only process about 110 bits of information per second. Understanding someone speaking to you requires about 60 bits per second. That's why we can't listen to more than one person at a time.
Multitasking isn’t actually doing multiple things at once. It’s rapidly switching between multiple things with incredible frequency. It fatigues the brain and results in much lower quality decision-making all around.
If you're feeling overwhelmed and like you're not moving the needle on anything, it's probably because you're trying to do too much at once.
Start focusing on one thing at a time, get it done and put away, and then move on to the next thing.