Weight gain

I have a normal BMI. I am now 8 weeks pregnant and have gained 5,5 pounds. It is my third child and for the first two, I put on 27 pounds in all for each.

Am I doing something wrong this time?

Why am I putting on weight so fast? I still go to the gym and I haven’t changed my eating habits except I can’t drink coffee and eat chocolate because it make me nauseous...