My employer messed up on enrolling me in health benefits. I was promised it would be fixed multiple times and I still don't have health coverage

When your supervisors or lower level HR reps are not correcting things that they should be doing (like health insurance), it is best to go over their heads to either the next level up, or directly to the manager or VP.  This is especially the case where you are facing serious issues and time is of the essense.  The changes created by the Affordible Health Care Act has created added steps for the employer to negotiate, but this does not excuse the company's failure to get this corrected when you need to get medical treatment now.  You should make clear the serious medical need you need to have resolved before incurring further medical complications (without giving up too much personal info) and give notice that you will need to purchase the medications by a set date and will expect them to reimburse you for this since it is their errors and failure to correct the matter that is causing the problem.  You need not be threatening with this letter or email, but make clear the seriousness and urgency of the problem, inability to wait any longer, and therefore their responsibility to reimburse you for these costs since they had ample to correct it