Ay oo, normal yan! A few of us mums got tetanus toxoid during pregnancy din, and the soreness usually lasts around 3-5 days kaya you're right on track. The arm might still be tender for a day or two more, but if it's getting worse, swelling gets bigger, or you develop fever, better text your OB agad para may peace of mind ka, your doctor can give you the go-ahead that everything's fine.