EMH: I understand your trepidation, but you're the Captain. You can't have a relationship with a member of your crew. They're all your subordinates. So, where does that leave you? The occasional dalliance with a passing alien? Voyager could be in the Delta quadrant for a very long time. A hologram may be the only logical alternative.
Before Janeway can have sex with one of these passing Aliens, the doctor has to sign off on compatibility issues that there isn't some health risk even if everything goes exactly right.
Also birth control is a monthly shot given by the Doctor, if he wasn't giving Janeway her monthly shot, then she was irresponsible or celibate.