I only took over-the-counter pre-natal vitamins. There are many different brands, the main thing is to make sure they have enough folic acid (check with your doctor for the amount). Also, take them right before bed so you don't feel the nausea they might cause. It always worked for me (and I felt pukey most of my pregnancy).
Also, I can't tell from your post if you're having a hard time swallowing it or if it's just upsetting your stomach. If you're having a hard time swallowing such a big pill, try any of the following:
1. Swallow with carbonated drinks. The bubbles help open your throat and make it easier to swallow.
2. Ask if you can either get a chewable prescription or if you could take Flintstones vitamins and an extra pill for folic acid (it might be smaller)
3. Cut the vitamin in half with a pill splitter and swallow it that way.
4. Crush it up and put it in a sweet, non-acidic drink (apple juice, grape juice, kool-aid, etc.)
I one or two of these suggestions helps you. Congrats on your pregnancy!! :-D