depressed: is it because of nofap?

Yes, this is perfectly normal. These are the withdrawal symptoms. It's going to get better soon.

Also read: http://www.yourbrainonporn.com/i-quit-using-porn-and-now-i-feel-worse

 

Yeah, and who knows what other issues in your life the nofap challenge is stirring up?

But assuming that your big issue now is battling temptation, it's easy to become depressed when we confront the sheer bloody relentlessness of these urges. You can get convinced that it's no use, it's too hard, our efforts aren't enough. But this depression, or discouragement, is the first signal of a fall brewing. It's a counter-movement in your mind undermining your nofap efforts and quietly leading you back to slavery in Egypt.

It make take you a few attempts to master this step, but you've got to recognise movements towards despair and exaggeration and lies. You need to fight to keep hope alive- that a better life free of this awaits you and remember that porn has given you nothing in life but waste and shame.