Sleep Anyone?

I know I've asked for tonz of advice lately, but I'm going to ask for a little more. Johnny started sleeping through the night when he was 8 weeks old. He was great for a long time, he'd just have problems when we were out of town, and for the first couple days when we got home. Now, he's almost 15 months and is awful at it. He wakes up 5-6 times a night crying, then yells Mommy, or Daddy until one of us comes. We've tried letting him cry it out, but he can totally outlast us, he's gone for more than 2 hours, plus we feel awful about it. We've tried the supernanny method and gone in and said nothing but "Sshhhh" and laying him back down, then waiting 5, 10, 20 min between each other time. Still no luck. We've been told that Passionfruit juice helps kids sleep, so we're currently trying that. We did it last night and also no luck. We're going to increase how much we give him tonight and see if that does any good, but I'm going crazy, we haven't slept in weeks. He gets a total of maybe 8 hours of sleep in a 24 hour period, including naps; and he's supposed to be getting at least 12. He doesn't even act tired half the time. I know a lot of people have younger kids than us and may be having the same problems, but I'm open to any suggestions at this point. We've got to find something that will work, he is so stubborn.....Thanks for reading this, sorry, just had to vent a little.