i have had this before also, you might first try using, and they do sell it over the counter a yeast infection cream that is for exterior not interior. If it started by your breasts, or like i sometimes get mine were my csection was reformed, and my belly over laps it, than i use this and it goes away. worse than to do is a- ignore it, and b- rub it, it only makes it worse, if the doctor gave you a med thats not working, it might also be shingles? similar to a yeast infection. hope this helped.
Yeah like the others said it sounds like a yeast infection. At the begining of my pregnancy (when my boobs grew quicky) I had a bad yeast infection under both of my breast. It can be very painful. It is very important to keep the area clean and dry. Bacteria love moist places. Since you sweat under your breast its the perfect breeding grounds for a terrible yest infection. Anyway here is was worked for me. First clean the area well. Then make sure the area is dry. Once it is dry apply baby powder under your breast. Don't wear a bra with under wire that may irritate the infected area.sports bras work great. Try this for a couple of days and see if it clears up. Once the yeast infection is gone start applying deoderent under your breast to keep the area from sweating to much. This is what finaly worked for me and I hope it works for you as well. If not see a doctor :)
Also I forgot to tell you is to make sure its not a staff infection. If it is you need to see a doc and he/she needs to give you antibiotics. IV is the best/fastest way. If you are diabetic go back to the Doc and tell him/her its getting worse right away.
My mother had this all she could do was try not to wear tight clothes and keep washing the area and apply fresh cream almost every hour. I can't tell you how many creams she when thru but it would come and go. she even had to stop wearing shocks because it would go around her ankels. It is a yeast Infection that can spread anywhere on your body. If you wear under wire bras this might be your problem. try to use a loose sports bra and clean under your breast and apply fresh cream as much as you can. Get a few sports Bras so you are not infecting the area again... Clean Clean Clean as you are killing your infection but DO NOT SCRUB... I know how you feel and I know what you are going thru just take it one day at a time.