coming during sex--please help!

My boyfriend and I have been having sex for about 3 months now and I still haven't come. He's my first sexual partner so this is all new to me. He does everything right (as far as i know) I just don't know why I still haven't and he feels bad about it too and wants to help. We talk about it all the time and we keep trying but I still can't and I don't know what to do. Has anyone else had anything like this? Any suggestions??