I've done some pastel paintings and I used to work in a frame shop. I don't think pastels are more difficult to frame, but they do take some special attention. Here's a few tips:
1. Make sure that your artwork is completely covered with fixative. You might want to give your pieces another light coat, just to make sure you haven't missed any spots and that you covered the corners, etc.
2. When you frame your pieces, be sure to include an acid free paper mat with your frame design. The mat will keep the glass off your pastel drawing (if the glass sits directly on your pieces, it can smudge your pastels and can also create some static between the glass and your working surface.). Regular matboard contains acid that can discolor and damage your artwork over time. An acid free matboard will not. You definitely want to have them framed correctly if you plan to sell your pieces.
I hope you find some frames that work well with your pastels. I'm sure they will be beautiful!