Lucy, boils or furuncles usually caused by bacteria called Staphylococcus aureus. They occur most frequently on the buttocks, breasts, neck and face. They might occur more frequently on the buttocks because the bacterial load is higher there, but it's not a given. They are usually treated with antibiotics (first ointments and then pills).
Usually that is all that needs to be done, but if the ointments/pills don't work the first thing I would do is to send some of the puss away to try and determine the cause of the boils and what the most suitable antibiotic will be. If the boils return again, we will then know that they are new ones and not just the old ones coming back (as we know that we gave the correct antibiotics).
You can try to prevent them from returning by using chlorhexidine gluconate soap, but usually it's not necessary. We now also need to make sure that there is no problem with your immunity and that there is nothing else wrong with you. We can then start giving preventative antibiotics for up to 6 months. If that doesn’t help, we start all over again because we missed something somewhere. If you have already been through this process, you need to find a good dermatologist. Good luck.