Can a hypochondriac convince himself that they have many stds and then start having symptoms?

Of course!: Hypochondriacs will often assume they have a conditon and imagine they also have the symptoms or try to produce them. They spend so much time trying to be sick, they cannot enjoy being well!

Hypochondriasis: People suffering from hypochondriasis do not purposefully intend their illness or their symptoms. They are highly sensitized to physical sensations, though, and may over-focus on or over-interpret them. They may be temporarily reassured by physicians' examinations or diagnostic tests, but the fears return fairly soon. Treatment requires collaboration between therapist & primary care physician.