Sorry to hear that you are struggling: There are a few things I tend to do during sad/blah days:

1. Take a nap (sometimes I truly need one and other times I just sleep to pass the time. It's not the best coping mechanism but it's hard to break that habit!)

2. Exercise. I can safely say that 100% of the time that I exercise, I always feel AT LEAST a bit better than before, oftentimes I feel a significant mood improvement. Physical activity is a natural anti-depressant, good for the body and mind. I highly recommend it.

3. Watch TV or Youtube.

4. Play computer games like WoW, The Sims 3 or 4, or Stardew Valley.

5. Do some chores around the house.

Sometimes I enjoy colouring or listening to music as well. Perhaps there are some activities you personally enjoy that could help to lift your sadness? I hope you feel better soon.