I underwent surgery (not a surgery)

Cf

I had an operation

The site of the incision/operation/surgery has became inflamed / has swollen up / seems to be infected and the stiches are broken / have broken

Ambiguity: I’d be careful with ‘because’ since you don’t mean to suggest that the broken stitches are the source of the infection at the site of the incision (the cause of the broken stiches), but that the broken stitches are evidence that an infection has taken hold

NB a more 'medical-jargon' – no ‘a’ or say ‘an example of medical jargon’ (or just plain articleless 'medical jargon' - but, further ... surely terminology rather than jargon - which suggests informal slang)

I’d head straight for emergency if I were you – ever heard of ‘golden staff’? (the horror, the horror)