Your boyfriend may have a severe skin infection that’s spreading. The redness, swelling, and pain—coupled with swollen glands in the groin—indicate that it might be a bacterial infection. To cure this, he may require a course of antibiotics such as penicillin or cephalosporin which can help to fight off the infection. It is important to seek medical attention as soon as possible to avoid further complications.

Staphylococcus aureus often leads to skin infections, boils, and even more serious problems such as bloodstream infections. It's caused by bacteria that may be hard to completely remove from the body. If the usual treatments like augmentin were ineffective in getting rid of the infection, vancomycin recommended by your friend is worth considering. Vancomycin is an antibiotic usually used as a last resort for persistent staph infections, especially those that do not respond to other antibiotics. When using vancomycin, it is important to follow your doctor's advice on dosage and treatment duration. 

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.

If you notice some vein-like structures on your penis glans, those are likely just normal blood vessels that have become more visible. You may notice this more during arousal. Usually, it’s not anything to worry about and doesn’t need treatment. However, if they are causing you pain or discomfort, or if they have appeared suddenly, it would be best for you to see a doctor so they can be evaluated further.