My body makes small babies

Hello all, when I was pregnant with my son who is now 8 months, I constantly had issues with him being small for his gestational age but yet I was always being told that my fluid was good, placenta and etc. I am now pregnant with a baby girl and I thoughtI was 21 weeks but shes measuring 19 and 3 days but yet everythingis fine... I dont understand why this could be happening to me. Does anyone else have this issue? Also I want to add- I developed Preemclampsia with my son and delivered him at 35 weeks and 4 days born 3 pounds 14 ounces, I was then put on blood pressure medication