Honestly 75 degrees should be fine. I usually try to keep my bottles somewhere between 70-80 degrees. I'll even let them sit lower at 65, but I wouldn't want them much hotter.
You're bottles haven't even been conditioning 2 weeks yet, so they are still young. I've had bottles carb up okay in 2 weeks, but you might as well give them 3-4 before worrying about it.
I'm wondering, are they bubbly, but just don't have good head yet? Or are they completely flat? Oh, another thing I forgot to ask, how long did you chill it before testing? A good 48 hours to chill will help the CO2 reabsorb into the liquid.