Its hard to say who is responsible for your bills based on your brief facts. Contact an AVVO attorney like me or someone else who can discuss this with you over the phone.
My answer to you question does not constitute legal advice. Only an in person or telephone consultation will result in an attorney/client relationship. Call me at (313)402-0853 to discuss your matter further.
You really need to ask an attorney in your state. I am pretty sure that the statue of limitations has probably run out. Also, if they did now have insurance, who would you sue? Sorry about your situation!!
You will almost certainly not be able to sue the drivers who caused the car accident in 2005. Michigan has a 3 year statute of limitations. Many insurance policies have a different date for contractual actions like uninsured motorist claims, assuming the other drivers did not have insurance as you wrote, but even then I've never seen anything longer than 6 years in a policy I've read.
However, you will still have a claim for no fault PIP benefits, assuming YOU were insured and you timely filed an application for benefits with your own insurance company within the one year time period to do so. Here is more information on this: http://www.michiganautolaw.com/no-fault/no-fault-benefits/application.php
You should run, not walk, to consult a personal injury attorney in your state to determine your exact rights, but I think you might be out of luck. If the accidents happened in 2005 and you never brought a lawsuit, it is now 7-8 years later and the statute of limitations (the time prescribed by law in which you must bring the suit or forever thereafter being barred from doing so) has more than likely run. (I believe Michigan has a 3 year statute of limitations). If you did start a lawsuit and it is over by judgment or settlement, it is unlikely that you can revive those actions based on continued medical problemens. There was also an a possible alternative given that the other vehicle(s) were uninsured, and that was to bring an "uninsured motorist claim" against your own insurance company and under your own policy, but that too would have had to have been filed/commence as soon as possible following the date of accident. Again, consult an attorney in your area, but you may be out of luck.