I am 33 yrs old and I cant climax with my boyfriend and its getting to the point I almost have anxiety about it. Why?

Thanks!! The sites did help me actually and I am relieved I found this site to refer to. My boyfriend turns me on and everything he does in bed is perfect but I just can't reach climax. And sometimes i'll get almost there then it goes away. Talk about frustrating n once I get frustrated that's it! In looking at all the posts in regards to this subject, I came across a book called The Best You'll Ever Have: What Every Woman Should Know About Getting n Giving Knock Your Socks Off Sex. I guess there is section in there about this subject so I'm gonna check it out!!