Is it normal to always feel sad?

well it sounds like you are unhappy of something and that something could be your job!

Everybody thinks they are happy with their job but sooner or later their "mojo" will burn out and they will wonder why they are doing this.

It happened to me before as I used to work in retail clothing store. One day I just thought to myself why am I doing this? arriving at work, doing the same thing, will not get promoted, talking to customers, doing duty and seeing same trash staffs? I nearly joined the army! Because I just wanted to do something freely like see people everyday, go out and talking to customers. So I ended up doing canvassing even though the job is FARKING hard, but it did help my mentality!

Now I've just found out about potential, living your potential! Doing what you love doing! So I'm gonna live my potential.

I don't know why you could be unhappy if you have a family so I'm sure it's your job that's making you feel sad.

Been there, still there. I've been depressed since the birth of my oldest child(7 years ago). I am seeing a psycharist and taking anitdepressants

Are you seeing a therapist? Many people say that the best treatment for depression (along with leading a healthy/balanced lifestyle) is a combination of anti-depressants and psychotherapy. Whilst anti-depressants help to alter the chemistry in your brain, they don't change the negative thought patterns that you have probably developed over the years. Therapy can help you do that. The most common and usually most successful form of therapy is CBT (Cognitive Behavioral Therapy). Through this method you learn coping techniques and ways to alter the negative thinking patterns that lead to your depression.

I'm no expert but I have/currently am going through depression right now so I am speaking from experience. I hope things get better for you. I know it is hard but just hang in there and you will find a solution that works for you :D

Try new things.It seems that doing the same thinhs every day bores you cause you dont do it with pleasure.Find out what can really give you pleasure and do it