i don't think 44/15 is unreasonable for a new rider but if you're experiencing knee pain - aside from bike fit as you mentioned - too high a gear ratio for you might have something to do with it. try dropping it and see what happens. 44/16 doesn't give you a lot of skid patches, though, so if that's a concern drop to 17. do you have / are you using a brake?

one other thing to consider;were you heavy into biking before you started riding fixed or has it sort of "re-introduced you to cycling" so to speak?