Sprint tri in 6 weeks time?!?!

Err... may sound a bit obvious, but START TRAINING

Difficult to give you anymore advice without knowing how fit you are to start with.  If you've got a reasonable base then just get out and start putting in the miles, there really isn;t any substitute for it.Have a look at the "couch to sprint" etc programs - if you have the base fitness to drop in at week 6 on the 12 week program , then go for that

If you're starting from couch potato, then you need to start with short sessions, and build up the distance (if you expect to finish, then the 10% rule for increasing training is out of the window)

I would suggest that you do more short sessions rather than trying to go for big long sessions - if you can then try to do 3 sessions of each discipline a week, 2 short sessions and one longer than the others.

It all depends on your present level of fitness.  Barring any significant physical limitations, anyone can ride 20Kms and run (or walk) 5Kms; it is simply be a matter of doing it at one's own pace.  And, as long as a person can do the swim leg without exhausting him/herrself, that person can complete a sprint tri.  Bearing this in mind, I would suggest that you concentrate almost exclusively on your swimming, especially if it is your weakest discipline.  Bike and run/walk once or twice a week and try to throw a brick in once in awhile.  It would be no use to push yoursefl too much at this point.  You would merely exhaust yourself before the triathlon rolled around or most probably hurt yourself by pulling a muscle or something of that nature.