I know how you feel - I'm pregnant with my first, and as horrible as it is to say... I didn't want to be pregnant at all. Found out I was pregnant when I was rushed to the hospital with abdominal pain, and they told me then and there. It totally threw me for six, as my partner and I had been using protection. I felt so completely disappointed in myself for letting me get pregnant, I thought my mother would despise me and throw me out (my partner and I live with her and my stepdad) for becoming pregnant at 20/21 (even though she had me at 18) and I also thought that my partner would just up and leave me. We'd only been together 10 months when we found out and I honestly thought he'd see me as some baby-crazed nutter who'd just gotten pregnant to trap him in a loveless relationship. I don't even know why I felt so depressed, but I did.
I buried it all, didn't speak to a single person about it and started considering a termination. In the end though I decided that because I don't believe in abortion (not for religious reasons but just my own personal view) that I'd have the baby, and deal with any issue that I had head on. And after about 6 weeks where I had a scan every week to check on the baby's progress, I started relaxing. My mother went into overdrive buying things for the baby, and my partner ended up telling me in no uncertain terms how absolutely ecstatic he was - and I started to believe him. And then finally I saw the baby's heartbeat for the first time and I was fine. I think a mix of insecurity and hormones dictated to me how I felt about my pregnancy at the beginning, and all of the normal questions like "How will I cope?", "Will I work?" etc. just plagued me, and to some extent they still do, just nowhere near as much as they did at the beginning. I'm writing this in floods of tears because I never told my mum or my partner how I felt, and it put so much extra pressure on me to try and cope.
I think the best thing to do would be to listen to your doctor and let him refer you to a psychiatrist - if that's what he thinks is best then it's always good to give it a try :) If it's not for you, or it doesn't feel like it's working, then why not write down everything that's worrying you in a book and sit down with someone you're close to, like your partner or your mum, and explain what you're feeling. At least they can give you reassurance about everything that you're feeling. At the end of the day, everyone needs someone to confide in, whether it's a professional, a family member, a friend or even sites like these where you can be totally honest about what you're feeling. There's probably millions of people who need to warm to the idea of a pregnancy, especially after you've relaxed and gotten into a routine, but just think about how gorgeous that little baby is going to be. And think about how wonderful your son is going to be as an older brother.
I really hope this helped, keep your chin up :) And if you need anything you just message me, I'm always ready to lend an ear :) xx