Hello, and welcome to Bluelight!
First off, whoever is telling you that you should wait 2 weeks between rolls likely doesn't actually know very much about MDMA. The suggested minimum is 1 month, and that really is a minimum, I usually wait 3 or more.
That being said, waiting a week between rolls one time likely won't cause you any damage. As long as you know that it's a one time thing for a special occasion, and wait a while before taking MDMA again, you should be fine, and you won't lose the magic from doing that just once
As far as 'preventative measures' go, your best bet is to just stay healthy. Eat well for the next week, exercise, and all that jazz. Also, invest in a test kit. If you don't know what that is, it's a series of tests you can do on a pill of ecstasy (or powder/rocks if thats what you get) in order to determine what is actually in the pills/powder/rocks, which are hopefully MDMA. There are a lot of adulterated pills/powder/rocks out there, and bunk pills can be a really bad experience. If you buy a test kit online now, it may actually get to you by the time you plan on rolling next, if not, you'll have it for next time. Google DanceSafe or EZTest to buy test kits and learn more about them (DanceSafe is better IMO, but I think EZTest is easier if your in Europe.)
Oh, and 5-htp does work, but it should be taken AFTER you roll. It can have negative effects on or even completely diminish your roll if you take it before hand, so just take it after to help regain some serotonin.
One last thing, if you want to try some fun things people do while rolling, take a look at the "E-Tard's Bible" It's full of fun stuff to do when you rolling, as well as some weird stuff. Also, Disney movies/music are really awesome when your high on ecstasy

Link to E-Tard's Bible:
http://www.bluelight.ru/vb/showthread.php?t=230119
Be safe, and have an awesome birthday!