My friend had a big follicle infection on his back, just under his waist, that just popped yesterday. He was given 2 different types of antibiotic and 1 anti-inflamatory drug to take. He said he had this problem 3 years ago at the same place. His doctor says that he may need.  Here are my questions:

1. What actually caused such an infection?

More than likely the infection is bacterial.  Without more information though it is hard to say if the infection resulted from an ingrown hair or if the pore simply got plugged trapping the bacteria.

2. What kind of treatment can be used (inside and outside) if we do not use antibiotics. I saw that you said the ozone works well for staph infection. Will it work for the hair follicle infection?

Yes, ozone would work great.  The ozone can be applied by cupping.

Another option is to take a raw potato, grate some of the potato and pack it over the infection for several hours.  The raw potato will help draw the infection out.

3. Could he be able to do something to prevent this from happening?

It depends on why it is happening.

4. Is surgery necessary?

Again, it depends on why it's happening.