So today i started playing whilst standing up, while i have played standing before i recently started doing it again and now my hand is sore and my arm is a bit sore too. 

Do you think im playing wrong or do i just need to get used to it? 

If it's just some muscle pain, then it just need to get used to it.
Same as sports exercising, first you are in pain, and before you know it, it's gone.

Yep, started playing bass a few weeks ago I got something very similar so i just pushed through it and it's all but gone now.