3 weeks late on period, negative test

hello. i am 3 weeks late on my period now. usual cycle is every 5 weeks, give or take a few days. i had my period on the 23 two months ago that lasted 3 days (normal for me) and now its been a month and 15 days and still no period. have taken three tests- all come back negative. i have been bloated for the last week, have tender nipples, slight cramping- but not very often and have had some hot flashes & frequent urination and have been really tired. could i be pregnant and its not showing up yet!? (used protection during sex, but not sure on the exact date in which it could be from-have a steady boyfriend. thanks for your help!