You have had a gall bladder surgery
3 months ago. If you have not had a follow up visit with your operating surgeon, please fix an appointment with him/her at the earliest.
There is definitely no harm in repeating an ultrasound
scan of the whole abdomen to rule out any bile leakage.
There may be a fistulous track too. The cause of fever
could be on-going inflammation in the abdomen.
Follow my suggestion and you should be fine soon.