Tinea Vericolor cannot be spread person to person. It is in the environment. Usually, it is found in hot, humid or tropical areas. But people who have low immune systems, are taking steroids, are pregnant, or ill can get it easier than others. Anyone with oily skin can get it too. Of course you should always finish the course of antibiotics that your doctor gives you because this can cause resistant bacteria or fungi or viruses, whatever you are being treated for. At this point you can get recurrances because this fungus is in the environment in which you live. The best thing is to keep your skin dry (not oily) and to use the topical shampoo and skin wash that they gave you. It is good that you are vegetarian as it is more healthy provided you are a non fat vegetarian (try to go to no cheese no oil). Just thought I would add that since I am vegan. I cook with water instead of oil. You can look up the site www.drmcdougall.com and he has a 10 days start diet that talks about a fat free vegan diet. But, it is harder to cut out the fat and cheese etc. It is a very very healthy diet. Read the what the people that have been on it say. Also he has a great book called the Starch Solution. Yes you should get some more ketoconazole cream and apply it to All the areas that have the problem. Be sure to wash your hands after and rewash the towels that you are using. Since it is on your butt you may want to wash your underwear more often. Again keep your hands away and don't scratch.
let me know if you have any questions.