The closest answer would be cytokines. These are proteins secreted by the immune system and basically cause inflammation. Some of these cytokines lower the threshold that pain neurons will start to fire at. This is why touching a part of the body that has been hurt is suddenly painful, where applying the same amount of pressure when the body is healthy would not produce the same response.

There's really not a a lot of indications to make these cytokines into drugs, but one, TNF alpha, has been made into a drug to help ramp up the immune system to fight cancer and has "pain" as a side effect. Most non opiate analgesic's block cytokines in one way or another which is how we get pain relief.