could i still be pregnant even i have negative blood pregnancy test?

my lpm was dec 23, 2008. i took my hpt when i was about 5 days dealy it came back negative and now im 2 weeks delay got my blood test done and also came back negative. but i still have have sign pf pregnancy like swollen breast, cramping, etc. can anyone have this king of experience and find out that their relly pregnant. pls share your experience. thanks
 
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