Rapid weight gain

So I was feeling good coming out of the first tri having only gained 2 pounds but once I hit the second tri I starting gaining fast! I am just over 17 weeks and for the last two weeks or so I've been gaining about a 1.5-2 lbs per week. Is this normal ?? Has anyone else had a sort of growth spurt like this? I haven't been eating or exercising any different so it's worrying me a bit!