I think you need to talk to a professional sarah, I can't think of a nicer way of saying this, but you seem a little obsessive about being pregnant? The reason I say this is because I became that way following an accident I had as a teenager which resulted in an unwanted pregnancy, but don't let any fears you have about becoming pregnant destroy your sex life i.e. not having one because you are scared of falling pregnant, unless of course you actually just don't want to have sex which is something different altogether.
I would think the chances of you being pregnant are very, very, very, very, very unlikely, but I would strongly suggest that you consider some sort of counselling as to why you feel that way in the first place xx