No simple, obvious answer, but...
it was a short PCT, for starters. I'm sure you felt great throughout your post cycle, yet that doesn't necessarily mean that your HPTA was fully recovered, thus low T is one possible explanation.
Wrt keeping 12 pounds of gain a few weeks after your cycle ended, that's too early to make a proper assessment. Glycogen + water is certainly one significant constituent of early gains in any cycle, and usually comes off pretty fast, so that may be the explanation, irrespective of the creatine, if it wasn't a hormonal or metabolic issue, or a combination of all three.
And why go from that cycle to cutting so soon? IME I need to pretty much force my body to accept the fact that it's going to be at a higher weight after finishing a cycle, and that corresponds to a good two months of eating at the necessary levels.