Is Pain With Periods Normal While On Birth Control Pills?

hi,
I was diagnosed with endometrosis a couple of months ago and now i've been told to take the pill without a break for 3 months and then take a break to let my period come and then go back on for another 3 months again till the next break. I am currently near the end of my second packet but i have been experiencing pain and a period for the last fortnight i wonder is this normal as it is affecting my social and work life. I don't know what to do as the pain is really getting to me. Its like a normal period but lasting two weeks is unusual please help if you can,
Thanks,
Laura