Would it be possible to ovulate 34 days after the first day of you lmp? To get your period aug 13th, but not ovulate until sept 15th?

It's possible. Not everyone ovulates monthly, not everyone has a period monthly. If your periods aren't regular, your ovulation probably won't occur regularly either. To determine if you're pregnant, take a preg test. To determine when you're ovulating to achieve pregnancy, check out the webmd site for an ovulation calculator or see your pcp. Over the counter ovulation kits are an option, but can be costly.