I'm going to sound like a blunt-dick (when I'm not like that?) with this but:
If you don't enjoy drawing, don't do it!!!!
If you get stressed, depressed or sad by drawing, then you have one of the following problems: A) drawing is not for you or B) you need to change your mentality.
The true is that drawing should be to evade stress, depression and sadness, is something you should enjoy and makes you happy. If you are getting the opposite then you are not made for this or you have the wrong mentality.
If the problem in other hand is your mentality, then stop working so hard and start to enjoy drawing, because there is no point in continue in this if you are not going to enjoy it.
We all get frustrated some times, we all feel that we reach a point we can't go beyond, we all have artists blocks, and the only way to overcome those is enjoying, is making drawing a game that always amuse you.