Joy is a conscious choice.
No matter how you put it, the way we feel is how WE CHOOSE TO FEEL. The concept that we are victim to our feelings, our surroundings and our reactions is erroneous.
When we are in the depth of suffering or depression, or even anger or discontentment or frustration, it is very difficult to feel joy. However, dwelling in the negative emotion, no matter how much we deserve to be in that emotion, is not going to help us.
Say we lost a loved one. We have to allow the sorrow and loss to express itself energetically, overcome all our being. But we don't stay there. At some point, sooner rather than later, we have to become the observer, acknowledge the feeling and move our attention to something joyful. In this example, where we lose someone, instead of indulging in loss and pain, we move our attention to the moments of laughter and joy we shared with that person. Or imagine them in funny situations.
If we are suffering from poverty, instead of indulging in fear and lack become the observer, acknowledge the feelings as being real and move your attention to gratitude and joy. Find things to enjoy around you. Stop feeling fear and lack.
It is very strange, and fantastic, but sooner rather than later, your circumstances will change into the ones you are enjoying the most.
But this secondary effect is irrelevant. What is relevant is that we are much more aware, and able to ascend to greater awareness when we are in a place of joy rather than one of misery.
This method goes against modern counseling and psychological schools of thought which make you indulge and explore the things that made you miserable. So, if these modern methods worked for you, then you might have to take a leap of faith to use Joy as your new medicine.