turbo nut question

[Vatche]

ive heard this is a problem that occurs alot but i searched and found nothing.....the nut on my turbo that holds it to the exhaust manifold....there are 4 total....one of them left corner closest to you when your looking at engine from the left side of the car...comes loose like weekly or every2 weeks....ive put several different types of lock nuts and washers....is there a special nut thats supposed to go there? i would love to know ....the stock one fell off and i dont know where to get that either....any ideas would be of help.....and just to let you know the first time i found out this happened i took everything out and put everything back in and then after 2 months the exhaust manifold nuts...just 2 came lose so i went to tighten them and one broke off the other is loose as hell i have to replace all the studs going into the engine that hold the exhaust manifold on.....any ideas for that too....did i do something wrong?