My bbt was elevated for almost a week when it suddenly dropped but I haven't started my period and now am late Could I still be pregnant or is it too late since the drop in temperature?

It is possible that you are pregnant. A decrease in BBT could indicated a decrease in progesterone. You need to have enough progesterone in your system to sustain a pregnancy, so if you think you are pregnant and your BBT has dropped, you should see a doctor asap (you can increase your progesterone level with pills or injections, but you may miscarry if your temperature remains too low).