It will make no difference. In the US, the standard
doxycycline regimen for chlamydia, NGU or cervicitis (the main STD reasons for prescribing it) is for 7 days treatment. Research shows that when 7 days is prescribed, more than half the patients miss doses or stop the treatment after only 4-5 days, yet the cure rates are the same as those who take the full 7 days of treatment. Although 14 days treatment is common in some places (e.g., the UK), even 7 days often is overkill.