Wodering what in the world I am putting into my body? Percodan or Percocet.

I have been using percocet(oxycodone5mg.,325mg.tylenol for almost a year now for chronic back pain.  My doctor gives me 1 tablet to be taken 4 times daily.  Recently, within the last month or so, I am finding that 1 does not work anymore and have been taking 2 at a time instead, which of course makes me run out of them early every month...I guess I have become quite addicted to them and have been purchasing more from someone I know on a regular basis. The first bunch I purchased seemed to be the same, but now I am finding that the ones I buy from this person seem to be weaker and are making my stomach upset.  They are generic and don't have either the name or the strength on them.  I am from Canada and the generic ones here have tec. on one side and then are scored on the other...these ones look like this, but I am wondering if they are in fact counterfeit or perhaps are percodan, with the asa in them instead of the tylenol and maybe are of weaker strength. My question is how would I know what they are?  Do the percocet and the percodan, which are of the generic brand here in Canada look the same or would they in fact look different and how would I know how much oxycodone is in them?  If someone could help me with this, it would be greatly appreciated...Thanks....Sheila.