could my mouth infection cause negative pregnacy test result

I am 27 years old and have very consistent cycles. Recently my cycle seemed shorter, and this month i missed one completely. I have taken 4 pregnancy test and they were all negative. I am feeling tired and sick to the stomach, my nipples are tender . I recently have a pus filled bump on my jaw which hurts. Could i be pregnant, and could the infection in my mouth give a false negative