Problems playing the low register on my flute?

Make sure that your flute has very recently been cleaned/oiled/adjusted by a COMPETENT flute repair specialist - not the the local * I can fix anything* band instrument person. You have leaks - either your fingers are not adequately covering the open holes, or you have leaks throughout your flute, which become more evident the lower you play. Perhaps this can be fixed through adjustment - or you might need some new pads. Yes, I am one of those folks who loathes Gemeinhardts - they have to be ONLY of a certain vintage and model to have quality, and that was decades ago. There are SO many flutes around today that are so incredibly better - and sell for the same price! - that you can do much better if only you have someone highly-qualified to advise you - a professional flutist and teacher, NOT the guy selling in the store!