Missed Period!!!!!

My last period was on 11/23/05, I have a regular cycle of 28days. My next period was expected on the 21st of this month, december. I still havent got it, which is not normal. I always get them on time! Me and my fiance are trying to conceive and we did have sex on my fertile days! Could this finally mean im pregnant? If I am id be about 4weeks and 2days today the 23rd. But im not sure if I sould wait till jan4 (id be 6weeks) because I dont want a false negative. I did take a test on the 21st and it wasn't morning pee but it came up negative!
I do know the hcg levels when pregnant...

3 weeks lmp: 5 - 50 miu/ml
4 weeks lmp: 5 - 426 miu/ml
5 weeks lmp: 18 - 7,340 miu/ml
6 weeks lmp: 1,080 - 56,500 miu/ml
most test are 50miu/ml sensitive!!

When should I take the test!???