How to feel happy after I have been happy
It is inculcating a habit of transcending that is trying to learn lesson each day. If you have been happy you have been in a position to learn lots of lessons and should be in a position to teach others.
Happiness state is temporary and so you would be sad tomorrow. When you are happy you can learn to withstand the sad moment which is likely to come and to overcome it with as ease this region needs to be strengthen even it is not in priority. Something more needs to be added in keeping happy in all circumstance and that is awareness.
Being happy in any situation is the crux when contentment could be a better word which is the outcome of sincere hard work and being focus in our desired activities which sometime we say as our dharma. If you are following the dharma you are already following a path for transcending needed at this age.