Pain is not normal particularly after being treated with IV antibiotics and then oral antibiotics
. Its been 3 weeks already! Have you had any fevers or chills recently? If so, I would seek immediate medical assistance.
However the fact that you are having pain is concerning to me, that your abscess was not completely treated, you may need drainage
with a needle if not already done. The fact that you are "gaining weight" in your abdomen makes me concerned that you are accumulating fluid inside you abdomen (either a leak from a prior drainage, ascites
My advise is for you to go to your primary care
or an urgent care to get an abdominal ultrasound
and check the size and status of the abscess, and make sure you don't have any free fluid within your abdomen.