iCloud security questions

Hi chaps ... a couple of questions.

I use the same password for my icloud itunes app store etc and on my iMac it seems to work OK.

However a dialogue keeps popping up on my iPhone asking for me to enter my iCloud password when I enter the p/word (on the moblie) it says it's wrong however I can get into iCloud on my iMac and it works.

So I thought I'd check it out and went to 'change password' and was asked the security question 'date of birth' I entered my dob and it said it was wrong. I then go to system prefs and 'Account details' and my dob is correct .... it's a real pain, can anyone help me out here please ?

Is it possible that I have, maybe, two accounts that are getting confused ?

Roger