Every pregnancy is different my sister is 38 weeks and has gained 7 pounds her whole pregnancy her baby is measuring 5 pounds 11 ounces so really she's only gained two
You gain weight when your placentia and baby grow. Also when you gain more fluid, you only need 300 extra calories a day which is about a pb&j sandwich extra.
You don't need to start eating more for the baby until like your third trimester you can google how many calories you need right now but I was 99lbs and im 135 now I've gained majority of that the past month
You're really early still, right about 20 weeks is when you start to gain. I gained a few here and there in the beginning, but at 20 weeks, I was still only 125. I'm 33 weeks on Monday and am now 148. Doctor told me today I need to cut back on sugary because I'm gaining too fast. P