I'm going to the beach on saturday, but I need some help.

It's about a 2 hour drive there... I don't get car sick, but I do sometimes get nauseated on long drives. I can take my Promethazine 60-90 minutes before to stop that, but it's going to be HOT that day and Promethazine reduces your bodies ability to cool down in hot weather. I will be in the water, but I need some advice on long drives,
Oo
and... My sleep schedule is messed up. I'm going to sleep at 12pm and waking up at 10pm. I leave saturday morning at 7:30 and come back at 4pm. I'll be nauseated from lack of sleep, but taking Promethazine against will mess up my hypothalamus. (That and I haven't been to the bathroom in 5 days will nauseate me)

What should I do? I want to have fun this summer and try to ignore my nausea and fear.