I didn't have morning sickness or any of the "classic" signs of pregnancy with my daughter. I felt awful until about 15-16 weeks with my son with sore breasts, nausea, queasiness, and mood swings like you read about.
Like the other poster said, if you have sex and miscarry, you probably would have anyway. So enjoy sex and enjoy being pregnant.
You will worry not matter what anyone says, it's part of the deal. Then when they are born, you will worry about different things.