Welcome to HCM.
Bruise on the right lower abdomen could be due to many reasons. Bruise in right lower abdomen can be due to appendicitis
due to gangrenous changes, pancreatitis
, ceacum infection , local trauma leading to muscle strain
or tear or could be due to fat necrosis
or any hemotological problem.
Based on the description given, The likely possibility in your case could be Local subcutaneous fat necrosis due to local pressure ( most likely possibility)or muscle strain or could be due to insect bite.
As you have mentioned that you have not strained much and had only soreness rules out the possibility of muscular and intestinal causes like appendicitis etc.,
Local hot fomentation and using medicines that contain serratio peptidase, trypsin and chymotrypsin
along with NSAID like Aceclofenac should help you. But please get an Ultrasound done to rule out other possibilities. Based on the result further course of action can be taken.
Wish you a speedy recovery.