Most of the few weeks pregnancy symptom is very similar to PMS because when I first fall pregnant, I thought my period was coming, but turn out I was pregnant... (I didn't get morning sickness and not everyone will have morning sickness in few weeks of pregnancy.) And I was 3-4weeks pregnant...When I went to the doctor, they explained to me that most of the few weeks pregnancy symptom is very similar to PMS... but then if your not pregnant then you'll get your periods soon.
Have you tried going to the doctor and finding out why you can't fall pregnant?