My daughter is always getting sick. She is almost two and she is always having ear infections and colds one after the other. Healthy children can have recurrent infections and be totally healthy. This is more likely if they are exposed to parents who smoke or if they are exposed to children in daycare centers. This is a very common problem, and your child's doctor should be able to help you sort it out.
Mood swings are unfortunately very common in our fast paced society.
Once the cause is found, the good news is that they can usually be treated effectively. There are a number of factors that you should consider. A wonderful website for review is the American Sleep Foundation. If reviewing the multiple sleep hygiene suggestions do not help, then I recommend you ask your doctor. My son is five and has a constant runny nose and it develops into a cough at night usually.