I would not use the Ampilox without a prescription from the doctor. If it is the wrong antibiotic for the infection, you could end up with a drug resistant strain.
If it is truly a boil, it will need to be lanced to drain the infection first.
As whisperwolf stated, this is not appropriate treatment. The infection may consist of bacteria which are not affected by Ampilox, or moderately affected, so you will develop a resistant strain. In addition the infection in a boil is usually encapsulated. Surgical debridement, which entails lancing and flushing the cavity with saline, often under a local lidocaine anaesthetic, is the treatment of choice, followed by a broad spectrum antibiotic, or ideally, an antibiotic that has been selected based upon a culture of the bacteria. The lancing and flushing are relatively painless, and usually necessary.