Cycling should release good endorphines and make you high.

Maybe after the good endorphines have subsided you are feeling a withdrawl, and through mental fragility you allow yourself to get moody and grumpy.

Are you sure its the cycling and not another external factor that is making you moody.

Is it your menstrual cycle that is playing you up.

Give your turbo away and get out in the fresh air, that will make you happy. Cycling in the rain is more enjoyable than riding on a turbo.