Am i going to get pregnant since i took nitrofurantoin while taking birth control and having unprotected sex with husband ?

Usually no worries: The current thinking is that except for rifampin, other commonly-used antibiotics (such as nitrofurantoin and many others) do not alter the effectiveness of birth control pills. This is likely presuming a person is not sick with vomiting or rapid diarrhea, or some other condition that decreases the absorption of a swallowed pill. One can look up: http://www.ncbi.nlm.nih.gov/pubmed/12063491