Hmm... Just like @Niko1nja said, you could try to 'do-something-else' (like trying to make music, or writting, or any kind of other activities that could involve 'creating' something else than art) or maybe give yourself a break from all this whole 'drawing-thing' to 'refresh' your head a little.
Nevertheless, I would also like to offer you my 'own' alternative: why not trying something as simple and calming as, for example, walking? Go put on your trainers, tie them properly, grab some headphones (preferably, in case that the sole activity of walking 'in-silence' itself could look 'too-boring' to you, all alone) and go take a stroll. Let the sunshine of the sun 'warm-up' your head, while the fresh wind helps you to make all those 'negative-thoughts' fly away out of it to never come back ever again, while also you listen to your favorite songs. How does that sound?
Myself, from time to time, whenever I feel 'down' or 'frustrated' with anything, I do that. And it works pretty good, so, I thought that it could be pretty good for you as an alternative, as well.
Give it a think, and in case that you try it in the end, let me know if it actually worked for you.
NikoN1nja
Neither do something else (idk, music for example) or just give yourself a break (maybe like 2-3 days).
chillzozen
im think of doin sm on reaper