Ok--to your original issue. Oxycodone is the active ingredient in OxyContin. OxyContin is simply an ER form,which will release about half instantly then the other half over then next 8-12 hours.
So...if you normally take 20 mg IR, you need more than 20 mg ER for similar effects. If you take 20 IR, taking between 30-40 ER (as directed) should keep you out of withdrawal.
Now, you went through 160 20mg oxy IR. That's about 3200 mg. You said you used them up in a little over a week. Guessing that to be about 10 days, that would mean you used about 320 mg/day. Even taken at 4 intervals that would mean you were dosing about 80 mg per dose. So---20 mg ER just isn't going to hold you as about 10 mg is released right away and the other 10 over the next 8-12 hours
Of course, you don't *want* to be dosing that high. I'm just illustrating why 20mg ER right now isn't enough. You may need to go higher for a few days then take less. It all depends on what you have left and how much time til your next appointment
With the time you've been on such drugs, this shouldn't be new to you.
And I'm not being mean, we all like a rush now and then, but that can't be your priority to the point your script is gone so quickly. Get on the ERs as prescribed next month. If you don't need the IR for breakthrough pain, save up a few and have fun with some IRs when you're close to your new script. ERs can give that rush too, but like I said you don't get 20 mg right away from a 20 ER
You're really not in a bad position. You've got the ER med which is better than IR for withdrawal