1. Creatine does NOT make you thirsty.
2. Creatine only causes INTRAcellular water retention (i.e. INSIDE the muscles, so you get the 'pumped' look) and NOT extracellular water retention (i.e. outside the muscles, so you look bloated).
3. Drinking 6 litres of water in a day can be too MUCH water, and definitely all at once is VERY dangerous, and you can risk 'drowning' your body.
4. Everything that you have mentioned are not common (or even heard of) 'side effects' of creatine. Being thirsty and getting headaches are actually symptoms of diabetes (not saying that you have diabetes, but do you have any health issues)?
5. Was this a ONCE off problem? Because if it was then I suggest (like everyone else) that it was something ELSE causing this. If it was NOT then would be the time to look at it more seriously.
6. There are many different types of creatine (i.e. creatine monohydrate, creatine ethly ester, creatine malate, etc.). I suggest that you try regular creatine monohydrate and just see how that goes.