My last period was 29th july and i ovulated day 20 (17th aug) does that make me 5 weeks? my period did usually come day 40/50

See your gynecologis: Obtain a pregnancy test from your pharmacist. You may be only 3 weeks pregnant. The rules for calculating the onset and the delivery dates are based on a 28 day period, which is not a valid method for you. The window of fertility may be up to 4-5 days, to confuse the issue further. If you are pregnanti, an ultrasound of your uterus may provide a clearer answer