You need to seek help from an attorney in your area on this matter right away.  I say that because now that you are 18 if there is a statue of limitations in your state - and I am not sure that there is - then it is running or it has ran.  You, yourself may have the right to bring an action for back support BUT there are generally some restrictions.  You must either have an affidavit of paternity or bring an proceeding to establish paternity. If you are not precluded from bringing the action for paternity then I think you can ask for back child support since your birth.  As for the medical expenses, that may remain to be seen.  Good luck.