21 day Progesterone levels...

My fertility specialist says if it's higher then a 5 you defiantly ovulated but everywhere I read everyone says it has to be a 30 or higher... Last month mine was a 13 and the doctor congratulated me but now after reading about it again I'm stressing out that the doctor has been wrong and I'm not ovulating or he's just saying that to get more money out of me because I'm not getting pregnant so I have to keep going back... When I've questioned him before telling him that I read something different about other situations he scolds me and tells me not to believe what I read... Should I question him about this or should I trust him since he's the doctor?