Exporting video quality loss

I am using the 30 day free trial of Adobe Premiere Pro CS6. I love it and made a great 15 minute video on my vacation this summer, however, when I export, I see a MAJOR quality loss in the video. Picture stills seem to be perfectly fine, but video is a lot worse. Before making the video, I did not convert all the videos into the same frame rates, qualities, etc. Is this my problem? How can I get around it so the exported movie looks exactly like the movie in full screen playback mode in the project window? (btw, i need to know soon because my trial is expiring.)

P.S. I am not using frame blending if that would make a difference.

via Video Editing Forums: Digital Director – Adobe Premiere, Premiere Elements, and After Effects http://www.videoforums.co.uk/adobe-premiere-premiere-elements-after-effects/42752-exporting-video-quality-loss.html