... or not gain much at all?

I noticed that I'm not gaining the typical 1-2 lbs/wk with this pregnancy, like I did with my last (as in, I'm 5 months along and gained less than 1 lb so far this month). Yes, I'm running after a toddler, but is the lack of weight gain a sign that I should be eating more? I'm definitely eating when I'm hungry...

I'm wondering if I need to bring this up to my OB, or if this is common with 2+ pregnancies.

ETA: I never lost weight due to morning sickness in the 1st trimester