If you test too early, then you may well get a false positive. If you're pregnant, hormone levels should double every 24-48 hours, and so waiting until your missed period is always better since the hormones will be higher than before your period is due. Just means your more likely to get an accurate answer.
ok so if i did test before then would i get a negative result
Sorry meant to add, since you say you have a 30 day cycle, it's most likely you're not irregular. So your next period would be due July 21st or so, so you would need to wait until then to test.
Do you have irregular periods? If so, and not sure when your next one will be, 2-3 weeks after intercourse is when to test. If you're not irregular then you take a test when your period is due...if it's missed. Tests can be taken up to 4 days before a missed period, but you're always better waiting until you actually miss one for the most accurate answer.