If you want to intentionally make yourself sick with a high fever, my suggestion would be to do some good while you’re at it. Perhaps you could go to one of the countries where people are desperate for clean water, you could help dig a well, while drinking the filthy water that they currently have available. You are sure to become ill eventually. If you don’t believe me, just ask any one of the mothers or fathers who has watched their own child die from one of the many illnesses that they have been helpless to save their child from.
If digging wells isn’t your thing, you could try one of the countries where malaria is prevalent. You could help hand out nets, vitamin supplements or food to children suffering from malnutrient (that is unless, they are so starved, they can not be saved and at that point you can offer to help bury them, once their little bodies finally give up and their heart stops). While there, make sure that you don’t sleep with a net, so that you can get bitten and contract malaria. Even with modern medicine, you will still have bouts of sickness for the rest of your life. I know, I have someone close to me that contracted malaria working to save the lives of children.
If you don’t feel like leaving the the country you’re in (whether the US or elsewhere), I’m sure they could use you as a volunteer at a free health clinic or nursing home. There are always lots of germs that are sure to make you sick, if you stick around long enough.