thats a lot of xanax, 6 mg. that alone should have gotten you somewere. I dont know much about promethazine, but I know it makes you sleepy. Zofran is an anti emetic, so Im assuming you werent trying to get high with it, maybe its inhibiting the xanax from working. try xanax and promethazine together with out the zofran, but Id wait a few days, xanax tolerance builds quickly an you dont want to waste.
Have you already built up a tolerance to xanax? Because that could be why you aren't feeling anything from it. I don't know anything about zofran or how it would effect xanax though. As for promethazine, I took it once, about half the dosage you did and it was horrible. I didn't get sleepy, I got drunk. Well I wasn't drunk but like I was stumbling all over the place, I could barely walk (and I was at school, it sucked) so I went home from school but I had extreme muscle agitation, I couldn't sit still because doing so made me feel like I was going to die. Like I tried to sit down and eat a bowl of cereal and I couldn't sit down long enough to get the spoon to my mouth and I'd hit the table really hard and just start screaming and pacing because I felt like I was going to go insane. Then I ended up flailing around on my floor screaming and hitting myself until I passed out. So, I don't know why promethazine had such a profoundly negative effect on me but I would definitely stay away from it. Since it isn't doing anythng to you maybe just wait awhile and give your tolerance a chance to decrease and try again with the xanax and promethazine. But watch out for that promethazine, is all.
promethazine is also used as an anti emetic. I have injections here just for nausea. And yes it will make you sleepy but its not much different than a low dose of valium or any of the diazapam group.