What Causes Infection Around The Incision Site Of Achilles Tendon Repair?

I am 2 weeks post op. for an achilles tendon tear. I was in a splint for a few days, then a cast. The cast was removed due to it compressing my calf and causing more pain. I may have aggravated my sciatica while keeping my leg elevated and and trying to adjust pillows for comfort. i have had just a splint since then, and two night s ago I started to develop a bad itch around incision site and on opposite side of ankle. I could not really scratch it so I took generic Benadryl 25mg to help me sleep. The next day I started to get a circumferential rash on my abdomen and back. The next night I took 50 mg before bed, and another 50mg when I woke up at 4:00 am due to itching. Went to doctors today and he thinks its allergice reaction to medication or something i ate. Am now on medrol dose pack. Should I be concerned about infection at wound. I normally heal without issues so I am a little worried.