ok, since you like the cells and molecules and finding causes graduate school might be an option. I did do grad school for awhile but I'll let someone with a masters or PhD tell you more about that track.
I would like to introduce you to some of the clinical lab sciences, which is what I currently do.
Basically the clinical lab science folks are the one's that do the testing in the hospital that the docs use to diagnose people. We learn A LOT about how the docs use/interpret the results too (disease pathways and processes that result in the abnormal lab values, treatments, drug mechanism of action, different leukemias, etc). A lot of people have the misconception that their blood gets drawn, throat gets swabbed, it goes on a machine and the answer pops out. In reality it doesn't really work like that.
It's something I'd never heard of and stumbled into by accident. I totally fell in love with it. It took me a year and half after my bio degree and it flew by. There are great job opps all over the country, pay is good, and there's more of a shortage than there is for nurses. You can go on to get your masters if you choose, or you can specialize in something like molecular diagnostics or virology.
Cool things I've gotten to do:
During my internship I went out and drew a blood sample on a patient for a CBC. I put the sample on the analyzer and noticed the counts were off. The machine flagged it as abnormal. I took a drop of the pts. blood, made a smear, stained the slide and put in under the microscope to do a manual count and differential. I noted a very prevalent abnormal lymphocyte type and some other features. I went and told the pathologist that I had a sample that looked like chronic lymphocytic leukemia. He agreed. Technically, only a physician can "diagnose" but often the lab folks notice the weird stuff and bring it to them to look at and officially diagnose.
I've examined culture plates from a blood culture and stool culture on a very sick, septic patient and isolated Salmonella and performed antibiotic sensitivity testing. Looked at the urine of 50 something women under a microscope and saw some nice happy trichomonas guys swimming around.
Other stuff we do, run chemistries, do immunoassays & pcr, blood typing, newborn testing, and compatibility testing, molecular diagnostics, fertility testing, and much more. Courses you'll take: hematology, immunology, parasitology, medical microbiology, clinical chemistry, bloodbanking, body fluid analysis and others.
Here's a link to more info (the pay cited is a bit low compared to what most of my classmates are getting starting out):
http://www.ascp.org/pdf/TheMedicalTechnologistandMedicalLaboratoryTechnician.aspx
If getting really down and dirty with specimens isn't quite your thing and genetics and molecular stuff is more up your alley you can do cytogenetics or cytotechnology. I don't do these myself but here's a link you can read up on it. Most of these programs have an option to do around a 1 year long intensive program after you do your biology bachelors so you don't have to start over from scratch. Pay is also very good and there is high demand for these people as well. The facility here has a one year program for cytotechnology after you complete a bachelors and at one time if they hired you they were forgiving the tuition for the program.
http://www.ascp.org/pdf/Cytotechnologist.aspx
From these to areas you can get involved in research if you work at a larger medical facility.
Lastly, I should mention Pathologists Assistants, which is pretty much a physician assistant to the pathologist (not just working with dead people). Most are Masters programs now. Path assts here make more than Phys. assts and Nurse Practioners.
http://www.explorehealthcareers.org/en/Career.119.aspx
http://www.pathologistsassistants.org/Default.aspx?s=whatisaPA
These are just a few things outside the traditional things most people think of doing in healthcare. I plan to go to medical school, but my lab science background rekindled my interest in infectious disease epidemiology and I'll be working on an MPH in Epi part-time while I work. Hopefully other people will chime in on other lesser known options as well. My biggest advice is to think outside the box and really do your homework before jumping into anything. You really never know what you might find. Good luck.
(for anyone else who might be reading this, other lesser know things include: dosimetrist, cardiac perfusionist* (really cool one)... actually, just go here
http://www.explorehealthcareers.org/en/Field.1.aspx and highlight allied health on the left menu for a dropdown list or go here
http://www.mayo.edu/mshs/ for a big long list of options).
