Is it normal to have a bowel movement only twice a week? do doctors know?

You're normal: Normal bowel frequency in america fits a bell-curve distribution--once daily stooling is the middle of the curve, but the normal range extends from 3 bowel movements daily to 1 bowel movement every 3-4 days. Assuming your bowel pattern has been stable for some time (in other words, has not recently changed from daily to every three days) then having two bowel movements/week is "normal" for you.