Generic term. Mood swings is a broad term used in many different ways. Apart from being a symptom of a major psychiatric condition other possibilities should also be entertained. Gender, hormonal cycling in females, personality style, life stressors, and coping skills are important factors. Eating right and exercise is important but not the whole story. A complete evaluation.And testing is warranted.
Psych evaluation . I would get a proper psychiatric evaluation to see why are the symptoms that we are dealing with. A proper history will bring out relevant family history o psychiatric conditions like bipolar disorder which has a strong genetic component. In regards to medication, mood stabilizers like lithium, Depakote and other newer antipsychotics are beneficil in decreasing the mood swings if needed.
Irritability. Mood swings and irritability sometimes go hand-in-hand. I am not sure how you're defining mood swings are they happening day to day tminute to minute hour to hour? What mood swings begin to interfere in your daily living and your relationships and work this is something that should tell you that in the evaluation maybe necessary.