I’m having hard time sculpting simple human head or anything in Zbrush.
These days i am spending almost all day and little time in the night, to learn how to sculpt in Zbrush, but it is so hard.
I don’t have drawing traditional background if that count.
And i have no idea or human anatomy at all.
I am getting very sad and depressed that, i cant sculpt, not even draw.
You are not the only one struggling with your art mate. That struggle is part of the process I guess
and it just takes time. Worki hard - yes but do’nt force it too much. Start small, take your time, take breaks, observe.
Enjoy every little progress you make to keep you motivated.
Though drawing skills and are not necessary to use a programm like ZBrush, background knowledge will help a lot.
So why not dig a little in the books of Andrew Loomis and alternate between drawing and sculpting.
Now go have some fun 
At 61 I had a hard time learning Zbrush but I put that down to my age, I found that watching video tutorials and having a couple of books on the subject most helpful. After about 9 months I can now do most things in Zbrush, not to the standard you find in the challenges or the top row, but good enough to make my wife say “Wow you made that”
The support you get on these forums is great, the best, if you should get stuck at any point. As to the human head the easiest way I found was by using the X Plane with a picture of the scull, then using Clay Buildup brush to insert the muscles. There are many tutorials on You Tube, seek out some done by Canned Mushrooms, they were most helpful to me, there are several links on the Zbrush web site to tutorials. Take a step at a time learn, as you go along things will drop into place, and things you once though impossible with ZBrush become second nature. Dont try to rush.
Wazer.