problem with moving music from mac to iPhone

Hello hope someone can help
I used to use i tunes on my pc and had no trouble moving music, playlists etc to my iPhone. now i have iTunes on my iMac and it won't let me move music to my iPhone because it says my iPhone is linked to a different account. any suggestions how to move my music. if i choose to sync my iPhone music it seems to say i will loose all music on my iPhone which i downloaded from my pc.

That's correct.

Why aren't you using the same iTunes account on your Mac as you used on your PC? Seems to me that would eliminate the problem ...

Thank you for the reply chas, I think they are the same but I will double check.
cheers ceej