My last period was aug.25.11. how many weeks preg. Am I my doctor seems not to know exactly and I'm tired of being confused about my own pregnancy. 1st time?

19 5/7 Weeks! 01/10. If the first day of your last menses was 8/25 then your expected due date is possibly june 1st, 2012! your OB will confirm these date by us best done during 2nd trimester, which amazingly quite often matches menstral start date.
19.4 wks. If you have a history of regular predictable periods every month you are approximately 19 weeks 4 days dated by your period. However, you need an ultrasound to assess the size of your baby and confirm the due date as often last menstrual period alone is not a very reliable predictor of how far your pregnancy has progressed. See a obgyn!
19 1/2 weeks. If 8/25/11 is the first day of your last period, you are 19 1/2 weeks pregnant, with a due date of 5/31/12. Since you mention there is some confusion, did you have an ultrasound which says otherwise (1, 2 or more weeks difference)? That might change your due date and cause some confusion, but we need more specific information. Please speak to your doctor about this.