If a girl that decided to date you for more than one time (believe me, she knew if she wanted to fuck you after the first day already) suddenly doesn’t want to see you again, trust me, it is not her job that all of a sudden has become so important that she cannot meet you and it is also not other responsibilities that rose up from nowhere.
It is you my friend. You had the chance to show her whether or not she will let you in and at some point you blew it.
Go through your last dates and try to find out what it was. What of your steps did turn her down. If you cannot figure it out, date another girl and be exactly like you were with the other girl. Look for the doomed moment. If that doesn’t help you always can go back to using one of human’s best things: talk to her. Tell her that you know it was you and that you don’t want her to blame “the job or the other things” in order not to hurt you. You want to know what you did wrong. You deserve it. You must learn and grow and she is there to help you (unless you did something so gross she even wouldn’t talk to you).