I just had iv antibiotics for three days. its been three days since the iv was removed but now the arm is achy and about a half inch bigger than the other. no redness, streaking, warmth. is this cause for concern?

Sometimes some minor swelling can happen, depending on what type of IV you had in, where it was located, etc. You should keep your arm elevated and see if it feels better and the swelling comes down. If you develop symptoms of infection like redness, increased warmth, fever, etc. or if your current symptoms don’t resolve in a day or two, then see your doctor ASAP. Good luck!

Apparently the IV infiltrated; That is, it perforated the vein and the ingredients leaked into and irritated the arm tissues. Follow Dr.F's advice which is spot on.