What Causes Weakness And Headaches After Taking Antibiotics For Tooth Abscess?

Hi, I'm 25 and I had a tooth abscess due to a failed root canal. The dentist put me on a course of prednisone (around 20 mg /day ) and antibiotics for 4-5 days. After that it's been a week but many times I feel weakness and my head starts to ache at nights many times - so i have to take a disprin. Is something wrong ?