10 days late, neg hpt with morning urine, lightheaded, nausea, could I still be pregnant? Trying to concieve

Take the test again. Being 10 days late with the negative pregnancy test does not mean that you're not pregnant. It is possible that you are pregnant but the only way to know is to retake the test with a good home pregnancy kit.
Family Practice. You may very well be pregnant false neg testing are common TIA early in a pregnancy. Don't be discouraged if you miss another cycle and testing is still neg. Then there may be hormonal imbalance. If you were on the pill it takes awhile to get regulated. I am a little concerned with the nausea and lightheadness. If this persists you need to be seen for this. It may be a sign of something else.