3 weeks after root canal retreatment i still have swelling and soreness. i just finished my 2nd round of antibiotics & steroids. is this normal?

It is unusual. See: Your dentist. Typically, any pain and swelling that was caused by a root canal infection clears within days, not weeks. There is still something going in. See your dentist to have the area evaluated again.

Not typical: It is possible that a small secondary canal might be present that got missed during the first root canal treatment. It is possible the root has a fracture. While most root canals are successful, unfortunately not all are. This needs to be reevaluated by a root canal specialist as opposed to a general dentist.

Root fracture???: If you have not had an apicoectomy (a procedure that is a minor surgical procedure where the dentist/root canal specialist makes a small opening into the tissue and bone where the end of the roots are and clean out the infected tissue, ) then you may have a fracture of the tooth or the roots. Often, then any retreatment will not work. I would consider a second opinion before getting the tooth out.