maternity leave

I really want to stop working because I am about to take my finals next month and need to focus on school. I don't know how to tell my doctor to put me out on maternity leave sooner. I'm 24 weeks and not due until end of Aug. Any advice on how to go about doing this. I am currently an LPN trying graduating from my RN program. I was thinking about complaining to my midwife about back pain etc but I can't be out on bed rest bc my company knows I am taking a clinical hands on exam....