You have to set your chosen route like immediately. The prostitution route and the thief route (where you keep stealing from the hospital) are the only developed routes that let you get blood pretty easily.
The problem is that if you visit the club, the character will be like "Oh, I'm just going to be a stripper, so I don't need to steal blood from the hospital or be a prostitute." After this, the main character will not prostitute and will not be able to visit the hospital. The MC will do this after any route is engaged. If you become a prostitute, she won't visit the club or hospital if you click on them. If you become a thief and continue to steal from the hospital, she won't be willing to prostitute or visit the club.
To become a thief, go to the hospital a second time (without visiting the club or becoming a prostitute!) and you will get caught by Deckard, the security guard. Then you come to an agreement where you do sexual favors for him in exchange for blood. There's an okay amount of content on this route.
To become a prostitute, select it in your activities list immediately, on the first days. Don't steal blood or go to the club! After selecting the activity, your character will wander down the streets, all scared to become a prostitute. You have to then get her lust up a little bit via masturbation until the first prostitution scene is triggered. The most sexual content is in the prostitution route.
Both the thief route and prostitution route provide plenty of blood.