Life can be a roller coaster at times. There will be highs and there will be lows. The important thing is not to overreact or think that everything has to be perfect all the time. Perspective is important. There is no silver bullet. There is nothing you can buy or pill you can take that will make you happy for any extended period.
Choosing to seek and have fun is a conscious choice. Rarely does it just happen. We all have moments of spontaneous joy we can remember, but this is the exception not the rule. I encourage you to make having fun a filter in your daily, weekly and monthly activities.