percocet 5/325 vs OXY IR and apap 325mg

for the last 3 years my doctor has had me on the percocet (5/325) 240 per month,

this month my DR. changed my meds to the OXY IR 5 mg 240 per month with the option of adding a reg strength tylenol with the OXY if i needed it.  What i have noticed:

1 percocet 5/325 relieves the pain for 2-3 hrs

1 Oxy Ir 5 mg makes me woozy, doesnt provide any pain relief

1 Oxy ir 5mg and a 325 mg tylenol (taken together): same effect as OXR ir alone

 What is the differance between taking a percocet or 1 & 1; they are the same chemicals right? any information would be great.