Feeling, as we mentioned the other day is one thing and having a sincere wish is another thing. So first to clarify on that, but to give you an example of something I did many years ago and occasionally still do. In my Compassion and Lovingkindness meditation I would take for my system all the people in my past I had friction with, all the so called "enemies," all the so called "difficult people." I would take them as a group. And I go through all of them one at a time. Now because I kept the same phrase and we've advised you all to keep the same phrase, it was possible that occasionally, many years ago in particular, I would be going: "May,...um...so and so...um...," and I would actually see these pauses in my sincerity. The phrase simply didn't flow.
In that way, I acknowledge, "Oh, I still have more to work on with this person." So then I would open up that person occasionally and remind myself of their Dukkha, remind myself what their upbringing was if I knew specifically. If I didn't I would remind myself how it hurts me, to hold back my compassion for this person. After some time as I did that, I could see that my phrase for them would flow without pauses, I could have a sincere wish for them because my wisdom was progressing, my understanding was progressing; concerning their Dukkha, concerning my Dukkha, concerning not wanting Dukkha.
So if you're not feeling compassion, remember that it is the sincerity of a wish which is most important. If you can see that you are not sincere in some of your wishing, then that's possibly a time when you would like to open up a Dukkha Reflection, so that you can understand more about the pain other people have, and then maybe open your heart more to them.