I'm 5"4 127lbs and this is my first child and I am 25 weeks should I be worried about my babys weight gain because im not showing big for 6 mnths?

1-2 ultrasounds help. An ultrasound study of fetal size knowing lmp helps. A baby is not considered to have growth restriction until very small (usually <10th %ile compared with others the same age). Having 2 ultrasounds can show the trend for fetal growth. Expectant mothers might want to take a look at my guides, including the one on ultrasound and this one on first pregnancy: https://www.Healthtap.Com/health_guide/27.
Discuss with OB. Since you are thin to start with and it is your firstbaby, you are not likely to show till 20 weeks or so.Now you are at 25 weeks, you should gain some wt for your baby .However, make sure you follow up monthly and follow your OB instructions.