Why can't I be happy in the pursuit of Nirvana?
I answer, since you tagged Tibetan Buddhism. However, personal practice is a serious matter and I believe you should ask a qualified teacher.


  After all we want Nirvana because we are looking for a being in a state of something eternal, Which is equanimity.


No, in Mahayana, we want to achieve enlightenment in order to be able to  benefit all sentient beings uninterruptedly, without  limitations of ours (death being one of them).

Instead of focusing on equanimity, rather train in being patient, content, and have few desires. First, there is less risks of being confused about what patience, contentment and few desires are. Second, it is more at reach for a beginner. Third, aversion to pain causes much unhappiness while patience opposes this. We suffer a great deal just because we have the notion that we would be better off without this or that, or having this or that. Discontent and desires also create much unhappiness.

Tibetan do not usually emphasize Anapana. The concentration factor is in general just a means for the mind to become stable and flexible, and then abide in virtue. Right now, it's difficult to study for a long period of time, or to meditate for a long period of time. Body and mind get sore and exhausted, there is pain and boredom. We cultivate the three factors of concentration, mindfulness and introspection by doing Anapana (or usually focusing on the mental image of the body of the buddha) simply to become able to abide in virtue for as long as we want. It is like opening your eyes to then get to see this and that. Unfortunately, there are people who engage in Anapana meditation and the like just to feel better, temporarily sheltered from their issues, away from their usual obsessive and discursive thoughts, etc. These are not wholesome motivations. Great teachers usually say: if you want to relax, take a nap. It's way easier than meditating.

Meditation should not replace the bottle. It should not be a means to bury your head in the sand or an anesthetic that makes your life more bearable.

There is no better way to damage the karma you have accumulated than:


Purifying by way of the four opponent powers
Restraining from non-virtue by upholding discipline (turning away from the 10 non-vritues, taking refuge and lay vows, etc.)
Abiding by wholesome habits such as not oversleeping, taking refuge six times a day, setting motivation before engaging in activities, dedicating after, offering food before you eat, offering drink (even water) before you drink
completing activities
Studying the teachings of the Buddha, because this will help you see things the way they are
Cultivating altruistic intention, opposing self-cherishing. This makes the mind vaster, open, and inclined in virtue.