How To Confirm Pregnancy?

I am trying to figure out if I am pregnant. My last period was Nov. 15th. I had sex on Nov. 11th. I have not had a period in 33 days. My cycles tend to be irregular but no more than 32 days. I have taken 3 tests in the last two weeks which have all came out neg. i don't have many symptoms. Just tiredness, a lot of minor headaches and sometimes light nausea that passes quickly. What is your opinion on this?