If you had a rash with a beginning HIV infection, the rash would not be rarely accompanied with one or more symptoms, which may include fever, malaise, headache, sore throat, swollen lymph nodes.
http://www.medhelp.org/medical-information/show/3149/Acute-HIV-infection?page=1#sec_28980
It sounds like the humid environment you reside in is to blame. If you see your doctor, he should be able to help out with the rash/
All sexually active people (especially those who are sexually active with more than once person) should be tested for HIV regularly as well. You should get tested just for a peace of mind, but I wouldn't expect a positive result.