What's my purpose in my temporary presence in life?

We often ask ourselves,what's the purpose of us in this lifetime of ours? No, I can never accept the fact that we're born, cooing in happiness, cry in sadness, all us need something in life. The question is,"What can  we do today? What can I do with my life today?  What? Can I do with my life to make it better today.How can I challenge myself? Considering that my daily lives are are thousand nails scratches on me, trying to rip my sanity apart.Leaving me helpless,hopeless, while leaving me watching life passing by all  by myself while life goes on and it waits for no one. No matter what shape  my heart was that day, or whether tear of my heart has warmth, it doesn't matter at all.
It's really a sad reality that I am living in. Sad, harsh, you name it, I have it's negativity. So, sometimes I find myself crying myself to sleep. Carrying bits and pieces of that sadness along.  I am glad many readers would wish me good luck, I thanked you all for the care that you expressed, but the truth is has something to do with:
1. my life- so wishing me that not to bring along my "work" related problems back home works, if they are "work related."
2. its nice when you go home with emptiness in your mind, leaving all problems behind. if only all my problems are all stemmed from work.
Time is now 8.42pm.I am 8 minutes away from fetching Isabelle from her Kumon. Then I'll go back home, hopefully to the warmth cuddle of my wife's loving hugs.