This past week I have been coming increasingly more grumpy and negative. I am aware of this and try to change it but for some reason my mood seems to be in decline.

I am usually upbeat and chipper, positive and helpful, but I just seem to be finding any old excuse to tell people to "fuck off" and be alone, at work and with friends, girls etc.
I don't know whether:
I'm too tired - i feel slightly tired but i've been worse
I'm overworked - I have been spending more time on screens and extending hours
I'm having a mood swing - I've had downturns before
incorrect diet - it mainly consists of meat vegetables and fruit, no bread, sweets or fizzy drinks

I guess I'm asking, does anybody else have phases like this? Is there anything obvious that I'm doing wrong? and what's the best way to come around again?