How many days late are you? As sprarah said pregnancy and PMS symptoms are so close it could be either. There are a few things that could cause your period to be late like stress or weight loss/gain. Even exercise can cause a late period. If you are over a week late and are still getting negative tests call your doctor to possibly get blood work done. Good luck.
You may have ovulated late so it may not show on a test yet.....or your symptoms could just be that your period is coming. Pregnancy and period symptoms are pretty much the same. Also since you think you may be pregnant you will notice more than you normally would. Wait a few more days and if still no period test again. :)