It's a tricky one.... because most pregnancy symptoms are very similar to premenstrual symptoms
The two suggestions I have that worked for me was:
1) Try to isolate the symptoms that seem somewhat unusual to you whether they be a symptom that you don't normally get with af.... OR a symptom that is usual but in an **EXTREME** form. eg: your breakout.... if it is extreme or unusual it may be an early prg symptom....
2) This one you may find harder.... every month I assumed I wasn't pregnant because I found that I would send myself insane looking for symptoms that weren't there OR be completely dysfunctional at work/home etc... It also was a buffer for the times that I wasn't pregnant as when I talked myself into believing I was pregnant... it took me days to recover after af arrived.
I know how hard it is so keep optomistic but make sure you give yourself a reality check once in a while....

You'll have a hard enough time convincing yourself you're pregnant when the test is positive!!!!