I Have A Severe Allergy To Antibiotics With A Component

I have a severe allergy to antibiotics with a component of Sulpha/Sulphur.I experience anaphylactic shock symptoms almost immediately and this results in difficulty breathing and I finally become unconscious.I have not had a severe allergic reaction in 30 years. However, in December my primary care clinic prescribed Cephalexin (250mg) to be taken 4 times a day for a urinary tract infection. The primary care physicians are aware of my allergy to Sulpha drugs.
On researching the drug's chemical components C16H17N3O4S x H2O I assume the S symbol is the Sulpha /Sulphur chemical. I am aware that the drug acts like Penicillin on a bacterial infection but the chemical structure is different.
I was in a remote National Park when I experienced anaphylaxis and luckily an ambulance was called and and I was given oxygen.
I would be grateful if you provide an answer before I take the matter any further.