Just as every pregnancy is different, the early symptoms can be different for everyone too. What you describe could be early symptoms of pregnancy, but it could have other causes as well. Once your period is due, or late, you will be able to take a home pregnancy test and find out for sure. It?s no substitute for a real test, but the free online pregnancy test at http://www.geocities.com/materni_tee/test.html
gives you an idea of some early symptoms (including heightened sense of smell like you describe)
Btw, I?ve heard opinions that some men have sperm that last longer than usual, which can throw a spanner in the works if you?re relying on the rhythm method.
Apart from the concern about gaining weight, would it be a bad thing for you if you are pregnant? I wasn?t sure if you hoped you were or not. Either way, best wishes.