It's normal. My guy couldnt at the beginning too for about a few months.
Did you mean that u have had sex with ur gf for 9 months and u used to be able to?
Oh in that case, I dont know for sure, but maybe u should try other positions, changing positions during sex stimulate other spots...Or have ur gf give u a hand job before having intercourse, just dont bring it to "cant hold it" stage.