As a Buddhist you should seek your happiness while working towards the happiness of others. Feeling bad is a self-indulgent activity done to justify inaction.
There is nothing selfish about being happy in the face of suffering, provided you are doing something to help address this suffering. For instance, you mention the suffering of animals. Very well, what are you doing about it? Are you a Vegan? Are you encouraging Veganism? Do you contribute or volunteer at any related causes?
If you aren't doing something to address the issue, then ask why. Why do nothing to materially fix the world (which benefits the suffering), yet go to such great lengths to make yourself unhappy (which benefits no one and adds to the suffering of the world -- you). Could it be that this "feeling bad" is a way of feeling better about not helping?
The mind often throws barriers to the path, and sometimes the best thing you can do is see through these barriers by asking what is REALLY going on.
So the Buddhist path is to seek your happiness while working towards the benefit of others. The right mindfulness component of this is to scrutinize your thoughts in this regard, in particular the thoughts propping up this "guilt".