You should definitely go to see your primary care doctor
about this issue as soon as possible. There are several different possible causes of this rash. Your doctor will be able to examine your penis and help figure out what additional testing might be needed.
Anytime there is a sore or rash on the penis, the first thing is to rule out a sexually transmitted disease. Most sexually transmitted disease will cause a classic form of ulcer or rash which is easy for your doctor to identify. Additionally, they will likely want to perform some urine or blood tests to test for the common sexually transmitted infections.
In additions, there are common skin conditions that can occur on the penis. These include eczema
, which are both inflammatory conditions of the skin. Also, sometimes, you may have developed an allergy or reaction to some chemical that your skin has come into contact with. Typically, all of these skin conditions on the penis can be treated with topical creams to reduce itching and inflammation.
Based on what your doctor finds on physical examination, they will be able to prescribe the necessary medications for you and also followup to make sure things are improving.