This sounds like dopamine deficiency to me, well, because I have it.
Lack of strong emotions, lack of real enjoyment, doing things only to fight boredom and not for the reward and pretty much just lacklustered feeling all the time. Common symptoms also include ADD (attention deficit disorder). If this is the case, there is no diet or anything that can help you. Exercise has been seen to be beneficial, but that is up to you.
There is a medication that increases dopamine, but it has a lot of dangers involved, and I wouldn't really promote that. If you feel like that this could be the case, go talk to a shrink.