hydrocodone drug interactions

I took my last oxycodone at 7:30 pm and my prescription was changed to Hydrocodone a few days ago. I was to finish the oxy and then switch to the hydro. I don't know how long I have to wait to start the hydro. I forgot to ask and there are no 24-hour pharmacies in my area. The local hospital won't give advice over the phone and I'm in major pain tonight. I usually take my oxy every 4-6 hours so when that time comes can I go ahead and take the hydro? Or do I have to wait unti lthe Oxy is out of my system? I know they're pretty much the same thing but I definately don't want to cause any weird reactions aside from the ones I already get from the pain meds. Please only add serious responses.

I am taking 450mg of Lyrica a day, 60mg of Baclofen a day, 1100mg of Naproxen a day, 200mg of Provigil a day, 10 mg of Uroxatral a day, 385mg of aspirin a day and was given a prescription of 500mg Hydrocodone to take 2 as needed for pain. I haven't taken any of this because I am concerned with the interactions it may incur. I have acute Multiple Sclerosis and a pinched nerve in my lumbar. Can anyone tell me?