Pregnancy weight gain

I’m a FTM, currently 21 wks 2 days and I’m starting to worry about my weight gain. My pre-pregnancy weight was 110lbs (approx. it’s been the same since high school, so I don’t typically weigh myself). At my 8 wk appointment, I was 116lbs. I’m currently 129lbs and gaining weight everyday. So I could’ve (potentially) gained 20lbs so far. I pretty much eat like I did pre-pregnancy (more fruits, veggies, and protein now), but I definitely don’t eat the “additional calories” that they say you should. I’m just not a big eater, so I’m really confused as to why I’m gaining so much. I was told to gain 25-30lbs, but I’m already almost there just at 21 weeks. Is this something I should be worried about? Could it be a sign of gestational diabetes or anything like that? How much weight did you gain by week 21?