Seduction university

Hi everyone. I’m really in need of advice. I’m 18, I’m 5′7” and 107 pounds. That leaves me with a BMI of 16.76. I fought very hard to to get to this weight from 160 pounds and now it seems impossible to put the weight back on. I don’t have an eating disorder or anything. I just quit consuming all the desserts, candy and soda everyday and joined swim team. These are things that no one should consume too much of anyway but this weight seems unnatural, despite my method of getting to it. Now that I’m 5 weeks pregnant, I’ve been trying to put on weight because I know this isn’t healthy for the baby. I’ve been eating right but nothing seems to work. It doesn’t help that I have been a major party girl lately. I never got into serious drugs but I was smoking a pack a day, drinking everyday and occasionally taking way too much medicine. I was doing this into the 2nd week of my pregnancy until I found out and quit cold turkey. I’m still having major cravings. I’m wondering what being underweight, a former smoker and user of alcohol and DXM will do to my baby. Have I already screwed it up and how do I fix it? I really need the advice here since I live in Utah and the Mormons here have the tendency to be judgmental and I can’t ask them. Also, the father seems reluctant to be involved. Any advice would be appreciated.