Troble picking up my iguana?

I bout my iguana like 2 weeks ago and it is about like 4 months well around there and I was trying to pick it up and it wont let me every time I put my hand in it just starts to whip me with its tail and then I keep trying to pick it up till the point were it just starts trying to bite me and then I just leave it alone so is there any kind of trick to calm it down