I've been using a mood hack recently which has been working great for me. It might work for you too but no gurantees as everyone is different. So the hack goes like this. Whenever you're feeling down or not particularly cheerful, force your face into a smile, a really big one and hold it for 30 seconds. Really tense up your facial muscles like you're flexing your bicep, but on your face. Empty your mind of all negative thoughts. At some point during the 30 second hold, you'll feel a little happier. The muscles will trigger a release of neurotransmitters like serotonin and other happy chemicals.