carbination question with first kegged brew

I am happy to say that I have taken the plunge into kegging. I kegged an AHS arrogant bastard mini mash kit last weekend as my first(and currently only) kegged brew. I put it in the fridge with 10psi and was planing on letting it sit for a week or so to carb. I pulled a pint tonight and it was perfect, great carbination and flavor. But then I pulled a second....FLAT. Why? Is this because it need more time? There doesn't appear to have any leaks now or before when I tested it. Any ideas?

10psi sounds low to carb a beer, even if its chilled. I though the rule is 30psi for 3 days

Well, I know that is one way, but I was going for the "set it at serving pressure and let it sit for a week or so" way. I have heard pros and cons for both, but I'm not in a rush and have heard more often than not, that this way leads to more consistant carbination.

I've been doing "serving pressure for awhile" with 10-12 psi. It works, but I've always given it at least 2 weeks before trying it. Give it a little more time.