What do you do when your feeling blue?

I am feeling pretty blue and moody today, I am not sure why, I have just started a Masters so I am a bit stressed out about that, I have just started a new relationship which is a good thing but I havn't had a relationship in years and it is alot to handle, I went out drinking at weekend and made a bit of a fool of myself, and I am feeling pretty run down, I guess it could be multiples of things or maybe just hormones who knows. The problem is with this low mood comes old urges and obsessions, I have been thinking alot about my weight lately anyway as I have just gone back on the pill and I am scared I will gain weight. I guess I just need a distraction or to do something to boost my self esteem but I just feel to drained to bother. I hate feeling so negative especially when there is nothing actually wrong! But I guess everyone feels like this sometimes and you just have to roll with it and hope it passes.