I don't know about South Africa, but rheumatic fever is very rare in the United States since antibiotics are so widely prescribed now. It's been years since I heard of a child developing it, and it is unusual for someone over age 15 to develop it. But with the underlying immune problems you have, any unusual symptoms are a reason to be concerned. Do you have a rash anywhere - red or pink, probably on your upper arms or chest? Rheumatic fever often presents with a rash, or with painful nodules under the skin. The chest pain you are having sounds a lot like pericarditis - which would be consistent with both rheumatic fever or a flare of your autoimmune disease. But if you have a rash or nodules, then RF would be a concern.
The problem is that rheumatic fever can cause many lupus-like symptoms, and there is no specific diagnostic test. So, like lupus, it is diagnosed through specfic criteria - both major and minor.
The major diagnostic criteria include:
Carditis (heart inflammation)
Polyarthritis (many joints involved)
Subcutaneous skin nodules
Chorea (Sydenham's chorea - emotional instability, muscular weakness and rapid, uncoordinated jerky movements affecting primarily the face, feet and hands)
Erythema marginatum - skin rash: skin eruption on the trunk and upper part of arms or legs: eruptions that are ring-shaped or snake-like in appearance
The minor criteria include fever, arthralgia (joint pain), elevated erythrocyte sedimentation rate, and other laboratory findings.
Two major criteria, or one major and two minor criteria, when there is also evidence of a previous strep infection (positive culture or rising antibody level -- ASO or antiDNAse B) support the diagnosis of rheumatic fever/
Treatment is usually antiinflammatories (aspirin and steroids) and antibiotics if there is a current infection. Since RF can cause permanent damage to heart valves, it's important that it be diagnosed and treated early. And even if it is not RF, your chest pain symptoms sound like possible pericarditis, which needs to be evaluated asap.