What does your belly getting bigger have to do with it? That doesn't happen for several months and there are many other symptoms which appear long before that happens. Have you missed several periods? If you haven't missed your period or had other symptoms then you are likely just gaining weight. If sperm joins with an egg there is a pregnancy which occurs. It seems unlikely that he could have enough on his finger to get you pregnant, but stranger things have happened. You didn't explain enough for a genuine answer. When did it happen? Have you missed your periods? Do you have other symptoms?