I started my period on a friday but accidently took the thursday pill (im taking yaz by the way), I hadnt noticed until today and I dont know if the pill has been doing its job.. HELP!!!!

I think all the pills have the same type/amount of hormones in it so you are fine. They just put the dates on there so you remember what day you are on and don't forget to take it. You will still be protected.

Wait...unless you mean you took a sugar pill instead of an active pill?

I'm not sure if I'm actually following your question.
If you're on your period, I'm going to assume you're on the sugar pills, which don't actually do anything. If you've mixed them up with each other, no problem. However, if you accidentally taken an active one, then it'll have no effect now, but you'll be missing on when it comes time to take it.

im sorry, the thing is every pill is the same and theyre all yellow (only 21 pills, yasmin not yaz, sorry)... does it matter?

I'm still not sure I follow. If you are saying you took Thursday's pill instead of some other day (and you are not on your break) then it doesn't matter, they both have the same strength. When they had different strengths, they color them differently.