Anyone know the "healthy" weight gain for 16 weeks?! :)

Je
Hi lovely mamas and mamas to be! 
I went to the doctor a month ago and she raised her brows when she saw that I had gained 7-8lbs since pregnancy. I started at 116 and now I'm 125, at 16 weeks.
I've had around the clock MS since week 6 and only carbs make me feel better. I was also restricted by my fertility doc to limit exercise to "light walks" the first entire trimester... So yes, I've inevitably put some weight on. 
Does anyone know the "right" amount of weight gain? Is there some formula? Wondering how much weight my mama-friends in here have gained...