It's a rare person that doesn't trigger a pregnancy test when pregnant. When it is 2.5 weeks after you had the sex you are worried about that would result in pregnancy (unprotected), you should get a positive pregnancy test if you are pregnant. Remember, symptoms of early pregnancy are not too significant and you get them because a build up of hormones from the pregnancy. These are the same hormones they test for to know if you are pregnant. So, if you don't have enough to trigger a test, you probably don't have enough to actually cause symptoms. All the symptoms you mention are that of PMS as well. Women can be late because of illness, stress, changes in routine, weight gain or loss, etc. If you aren't sure when that 2.5 week time frame is, you can test once a week for the next two weeks. That should do it to know if you are testing too early for pregnancy. Let us know the result, okay? good luck
If all of the home tests you did were negative, it's unlikely that you are pregnant. I guess it is possible that you had a chemical pregnancy, but those are so subtle and go by so quickly that they do not produce symptoms (other than a late period). Certainly not breast changes, mood swings, etc. As Specialmom said, it's more likely to be PMS than a pregnancy. If you simply don't want to believe it, though, you could go to your doctor for a blood-based pregnancy test. They are impossible to fool.