on average, i probably drop 2 pills in a big night out once every 2-3 months with pre/post loading......and on average i smoke 4 g of weed a week. Being a long term and reasonably heavy weed smoker, i can guarantee after a few years of use you do start to develop some noticeable short term memory loss, which can really work against you in an exam style situation, which is why i am planning on reducing my intake to a much more moderate level as my nye resolution. I would highly recommend you go on a self-imposed detox period over your yr 12 exam period, this is what i did and i did exceptionally well.
You say you drop 2-3 pills a month, again i would say this is a little too much for someone entering yr 12.....and probably too much for someone your age, generally the more mature someone is, the more likely they are to practice moderation, and not dump excessive amounts of pills simply because it's fun, save the pill popping for uni life i reckon.....mdma is not like weed, it won't work perfectly every time....and can also have this effect of making people avoid their daily duties and ignore those things which are important.....like study.