For this type of condition, one should consult a dermatologist. The rash may involve several causes, which include allergic reactions and skin infections. In case you have already had STI testing and treatment, the rash should be diagnosed by a specialist.

Your wife is likely to have an infection at the injection site. The symptoms such as heat, pain, and redness are caused when the bacteria get in. The area needs to be cleaned gently and the healthcare provider must be consulted. Antibiotics may be recommended to eliminate the infection. Do not use ice or cover it up without advice as it may aggravate the problem. 

The dermatologist will first need your family history and trichoscopy examination for the evidence of vellus hairs. Then they might begin their treatment with minoxidil, micro-needling and Growth factor injections. If no improvement is seen however, then they will suggest hair transplant.

A rash affecting your intimate­ areas may indicate a yeast or bacte­rial infection. This condition is widespread, so the­re's no need for e­mbarrassment. For treatment, a doctor could re­commend an antifungal cream or antibiotic ointment. Maintain cle­anliness and dryness in the affe­cted region. Wear loose­-fitting garments. Refrain from scratching to expe­dite healing.

It seems you're showing some alarming symptoms. The red bumps with black centers may be due to folliculitis (inflamed hair follicles), burn or a mild fungal disorder. The itch on your scrotum is probably caused by possible irritation or it is an allergic reaction. A thorough cleaning of the body and a proper diet would be great as well, but it is the best choice to visit a health care professional to know the correct situation and also get treatment. They have the capability to provide the relevant care and the necessary reassurance. As health should be your priority, always think about getting assistance when you have a problem.