My Wife Is About A Week Past Due For Her

My wife is about a week past due for her period. her breasts are sore and she has some symptoms of early pregnany but we have taken 3 tests all coming back negative...our last pregnancy she had unusualy low hormone levels at first. She is on the nicotine patch losarten synthroid she is diabetic. I am really just wondering if the nicotine patches could be causing a false negative