What Causes Numbness In Hands While Holding Things?

Hello Doctor, My Age is 30yrs, weight is 65kgs & no specifis medical history. I hav a 3 yrs old daughter. I have a numbing sensation in my fingers whenever I try to hold something or write. I had this condition when I was pregnant & situation was much worst then. I could not even make a fist for a long time. Within a minute or so I would get numbness. After my child was born this conditon improved a lot but not completely. Whenever I sit down to write with pen after sometime the numbness returns. Though its not very acute but then I have to stop writing & jerk my hands for a few time to relieve me of the pain & then resume writing again.Else the pain would extend to my elbow. This has been going on ever since the birth of my child. At times even when I wake up in the morning, there is numbness in my fingers but as soon as I start moving around home to do stuff the numbness vanishes.The numbness can be caused by any of these - writing with a pen for about 30/45 min, early morning, holding a tray in both hands position or an umbrella, or holding mobile just after getting up in the morning. I also get pain in my hip & knee joints.Some how things got worse just before I became pregnant.While sleeping all of a sudden there would be a shooting pain & waking up I would realise that I was sleeping by bending my knee ( I exactly dont know for how long) & I had to make my leg straight to get rid of the pain,& while trying to do which again gave me tremendous pain. Pregnancy gave me a relief . I never had that kind of pain again. Even after my child s birth, I did not get it for a long time. Then suddenly one day I again got the pain but they were not as frequently as they used to be. Now a days whenever I sit crossed legged (or in any position where my knee is bend) after about 20/30 min there is a little pain in the hip & knee joint & I have to change my siting position. I want to know why am I getting these pain/numbness?What is the reason & its cure? Or you can also advice me to check up with which specialist. Thanking u in advance.