Sorry you're experiencing this. I know that fasting makes you more mentally alert which tends to help with depression, never heard of it doing the opposite though.
My guess would be that since you're more aware of your feelings and your surrounding, past situations that were overlooked before are more obvious now due to the fast b/c when we're fasting we are more intact with reality since we're not distracted by many other things...perhaps there were other things going on in your life that you weren't seeing clearly before that may have been depressing and now that you have a better observation on them the issues are apparent, hence it being depressing...Hunger itself can be depressing even when we're trying for something rewarding.
This is all guessing sorry, I don't know what I'm babbling about or much about fasting really...hopefully someone more experienced can chime in? Take care.