Hello again,
I can't really tell you what project to do, because you need to pick something that you are interested in. Since you are doing a highly competitive project, your idea should be unique from others. For instance, don't just copy someone else's experiment, but if you are interested in that topic then use their project as a jumping off point. I think maybe you are caught up on finding the "perfect" project? There isn't one, but you should begin with what you think is interesting and what you want to learn about. You might want to start by:
1. Choosing a broad topic: Medical science
2. Narrowing it down by looking at the articles and suggestions I have given as well as other resources
3. What have you learned about in school that really makes you want to crack open your science book to learn more about?
4. What have you heard in the news recently that you didn't understand or what you wanted to know more about?
5. What is a topic that you think would have an impact on medical technology or health sciences?
Read some articles from Scientific American, Discover, Medline Plus (
http://www.nlm.nih.gov/medlineplus/magazine/index.html)
Look on this site for current medical topics, research, studies, etc. to get an idea or topic of interest.
http://www.nlm.nih.gov/ and
http://www.nlm.nih.gov/portals/researchers.html
Also, keep in mind your timeline. When is the final project due? That may limit what kinds of things you will have time to do. At this point I think you need to start by researching your topic. When you read articles and you find yourself saying, "What does that mean?" or "How does this/will this impact the medical field and/or patients?" "What is a possible solution to this problem?" "What have previous researchers done in regard to this topic, and what do we need to study to find out more?"
You said you have been to the state level twice? What projects did you do then? Why don't you advance one of those projects, or extend your study?
Hope that helps. I know you can find something you're interested in studying and creating an experiment for.