It is very unusual for the fertile days to start so soon after a period ends. Do you normally have smaller cycle? less than 28-25 days? If your fertile days indeed fall so soon after your period, and you had sex right after, then chances for pregnancy are high.
ANY line on the home preg test within the time prescribed by the test manufacturer is positive. Most early preg home preg tests show very faint lines anyway. Also, the fact that you are now 6 days late for your period shows that the chances of you being actually pregnant, are higher!
Wish you all the best!