Your problems with sitting are due to your body-and-mind not being stable enough; irritability makes even regular activities difficult, let alone sitting meditation.
At this time, I suggest you to approach your problem two ways: from physical perspective and from psychological perspective.
Physically, you need to train your body by learning deep breathing through the following exercise. Walk very-very slowly, making one inbreath for about 4 steps / 10 seconds, and one outbreath for the next 4 steps / another 10 seconds.
Psychologically, forcing yourself to sit is not a good idea. Instead, try to develop a habit to sit every day, but not for a long time. Start sitting for only 20 seconds, and slowly add a few seconds every day, so you only sit as long as you really can. Again, the most important is to do this regularly. You must be determined to give up any other activity in favor of your daily sitting.
You know what? Habits, habits, it's all about forming a habit. Start small, exercise for six months until it becomes a habit, then practice for 10 years, one life, next life -- and you will have a different temperament.
Whatever requires conscious control in the beginning, becomes natural and effortless once the habit has formed. Eventually, you will be able to set your mind in a natural state -- and you become a Buddha!