Talk to Gynecologist on Pregnancy, Gynaecological Assistance Required

Hey. I am by now 20 weeks pregnant and I am concerned if my baby is healthy both mentally and physically. I did had 2 ultrasounds and my doctor said everything is fine. But I am still worried due to the fact that I didn't had any healthy diet for all these 20 weeks and I sometimes miss taking my folic acid too. I wanted to take AFP tests ( I read about this test over Internet) but my doctor didn't recommend me. What should I suppose to do now? Is it okay of my doctor to not to suggest me this test or should I take this test on my own? Please suggest. Your mentoring will highly appreciated!