Hello, I Realize The Stupidity Of This Question- But Need

hello, I realize the stupidity of this question- but need advise as I am a little concerned- I had m period on 11/22 I actually got my period early in November(22 days) it averages about 25 anyway- I had complete un protected sex 18 days later- Today I am on my 31 st day with NO PERIOD 3 pregnancy tests NEGATIVE and I completely feel as tho I am getting my period but it is not coming it should of came already as I have had PMS for over 7 days now- I am 45 years old.. and did not think I could really get pregnant... what are your thoughts