Husband sought testing for STDs--does this mean he has been unfaithful?

I discovered a prescription from my husbands PC physician for HIV and Hepatitis testing. Not only was I unaware that he went to the doctor, but we had both been tested before we were married last year and I believed we were both disease free and monogamous. Also, I am six months pregnant and should mention the scripts were among his papers where I would not have "accidentally" stumbled upon them. Do I confront him about this finding? Is there any hope of him being honest with me regarding his actions?