Cephalexin Monohydrate and skin infection

I had a skin infection on my lower legs and was prescribed Cephalexin Monohydrate. I took it for 6 days, 4x per day, then stopped. I was supposed to continue on 2x per day for the next week.
I started itching at the top half of my buttocks and it quickly spread all over my back, chest, shoulders, arms and onto my scalp. Small lumps or hives and red blotchy skin nearly all over my old body. The itching was driving me crazy. I didn't know where to scratch or rub next.
My doctor couldn't see me for another week so I went to see another doctor who prescribed Phenergan (promethazine hydrochloride) tablets and Celestone M (betamethasone) cream.
Relief came within 24 hrs, I went through 4 days of hell and while still itchy on the 5th day, it was getting better. I also used ionil T ( a medicated shampoo ) for my scalp.
I have never been allergic to any drugs before this monster
This antibiotic should come with a warning

Was prescribed cephalexin (Kaiser) for a broken skin infection on my leg from a sporting accident. It was pussing and not healing well. Started taking cephalexin immediately after leaving the pharmacy. Within a couple days, my skin infection was not any better. Hives and bright red dots appeared on my chest, my arms, and my legs. Itching was intense - I couldn't sleep - would wake up in the middle of the night totally on fire - but I was told to stay on course by the nurse at the pharmacy and finish the bottle as I wouldn't want an antibiotic from losing its hold on the stronger existing bacteria. The hives, in the form of red patches, bumps, and streaks were visually traveling through my body and hives would break out. I resisted itching. Then one morning I woke up and my entire chest had a huge patch of hives taking up the entire space between both nipples and from the top of the rib cage to the collar bone. It was ridiculous. One week in, I called my doctor and went in for a check up. Instead of prescribing another class of antibiotics, my second doctor (and opinion) opted to stop taking the medicine all together. He determined the hives were an allergy to Cephalexin.