"Why do I always feel unhappy" can be more than a temporary situation.
There are actual physical maladies that can leave you feeling unhappy.
If these feelings are not addressed and the cause is not determined than you may spiral into depression.
Everyone feels unhappy one in an awhile, but if your situation does not warrant the feelings you may have other things going on that are bringing you down.
Here are three main causes for wondering "why do I always feel unhappy?"

1. Nutrition- Eating has really one primary function; it is to feed the body necessary nutrients that are key to proper bodily functions.
   Empty calories or foods that are not rich in nutrients can affect your mood negatively.
   Eat foods that are full of nutrition and ask "why do I always feel unhappy?" less.
   
2. Hormone Imbalance - your hormones control your happy! When your hormones are out of whack so is you're happy.
   To get your happy back you need to regulate your hormones so that they are balanced.
   Once you get your hormones under control you will quickly notice that your mood will improve.
   There are many different things that affect your hormone levels.
   Natural aging affects your hormone level, stress and a host of illnesses.
   Find the cause and find the cure!
3. Disease- when you are ill or you are suffering from a disorder, you may find yourself asking "why do I always feel so unhappy?", you may not even know that you have a disorder or a disease, and feeling unhappy is the way that your body is sending you some signals.
   If you suddenly feel unhappy all the time and you feel your situation does not warrant it, go have a physical so you can pinpoint what is happening.
   

You should be able to live your life without having to wonder "why do I always feel unhappy?" Find the cause so that you can start feeling better.