Hi! Honestly the only way you are going to get a false negative on a pregnancy test is if you take it very early in pregnancy (we're talking under 14 days after you ovulate). Anything over 16 days past ovulation will give a positive response. The time *after* ovulation is NEVER more than 16 days unless you are pregnant (or have a luteal cyst). The time *before* ovulation can vary a lot due to stress, illness, etc, but the time after doesn't stray more than a day or 2 from your "norm". If you have taken several tests (I'm assuming they weren't all in the same day and you spaced them out over a few days/weeks) and they have all been negative then you aren't pregnant. You just aren't. You can request a blood test if you want (just go to your gp) but it will still be negative.
Having light periods is just that - light periods. Are they still regular? There are other things that can cause nausea and dizziness besides pregnancy. If I were in your shoes, I would go see my doctor. I would want to know what was going on with my body.
How far apart did you space the pregnancy tests? What tests did you use? When was your last period? Are your periods regular? Do you know if you ovulated? Are you on any new meds (your symptoms could be side effects)?
Here is a web page to read about false negatives:
<a target=_blank class=ftalternatingbarlinklarge href="http://www.early-pregnancy-tests.com/missed-period.html">http://www.early-pregnancy-tests.com/missed-period.html</a>