I don't believe you're pregnant but you might be.. Personally I think not.
So did you fool around June 30 or July 30? If June 30, you should be in the clear.
Even if it was July 30, I'd say it would be extremely unlikely that you could get pregnant the way you described, but I suppose it's not impossible. Additionally, if you're fairly certain you didn't ovulate till the 5th, it would be unlikely that the very few superhero sperm that might have made it past your cervix would still be alive to fertilize your egg.
If you O'd around the 5th, then August 12 was probably a bit early to get a positive result if you do happen to be pregnant. You should be expecting your period in the next few days if you have a 28 day cycle, so if you're still worried and haven't gotten your period, I'd test again.
Good luck.