21 weeks rapid weight gain?!

I am 21 weeks pregnant with my 3rd boy and started my pregnancy at 108 pounds. In the first trimester I gained no weight and starting about 2 weeks ago the weight is packing on rapidly. On August 6th I was 116 and today August 18th I am 122.6! Is this normal? I feel like everything I eat, it ends up showing on the scale. I am trying not to obsess over it but its getting hard not to! Do any of you mamas have any answers? The docs office is saying it's normal and could be extra fluids. 🤔