Yes, human heads are hard. My advice is to sculpt some skulls. Seriously. Make yourself study some anatomy and reproduce some in scale. Then when you get a skull like you like it, sculpt a face onto it. That will make you scale your details better than anything else. For now, you are trying to interpret so many layers of stuff, much less hone skills. You'll get the details, just focus on the anatomy first. There are many tricks to help you with it. You'll get it. Keep it up!